U.S. patent application number 13/926126 was filed with the patent office on 2013-11-07 for pump with suction and pressure control for dry particulate material.
The applicant listed for this patent is Nordson Corporation. Invention is credited to Terrence M. Fulkerson, Stephen G. Nemethy, Jeffrey A. Perkins, Joseph G. Schroeder, Terry John Thompson.
Application Number | 20130294848 13/926126 |
Document ID | / |
Family ID | 37250088 |
Filed Date | 2013-11-07 |
United States Patent
Application |
20130294848 |
Kind Code |
A1 |
Fulkerson; Terrence M. ; et
al. |
November 7, 2013 |
PUMP WITH SUCTION AND PRESSURE CONTROL FOR DRY PARTICULATE
MATERIAL
Abstract
A pump for particulate material includes a pump chamber wherein
material flows into the pump chamber under negative pressure and
flows out of the pump chamber under positive pressure. A plurality
of pinch valves are provided to control flow of material into and
out of the pump chamber. The pinch valves are operated independent
of each other and of the pump cycle rate. A modular design of the
pump is provided. A pump control feature is provided for air flow
rate control during positive and negative pressure conditions.
Inventors: |
Fulkerson; Terrence M.;
(Brunswick Hills, OH) ; Nemethy; Stephen G.;
(Lakewood, OH) ; Thompson; Terry John; (Wakeman,
OH) ; Perkins; Jeffrey A.; (Amherst, OH) ;
Schroeder; Joseph G.; (North Royalton, OH) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Nordson Corporation |
Westlake |
OH |
US |
|
|
Family ID: |
37250088 |
Appl. No.: |
13/926126 |
Filed: |
June 25, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13444321 |
Apr 11, 2012 |
8491227 |
|
|
13926126 |
|
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|
|
12774951 |
May 6, 2010 |
8167517 |
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|
13444321 |
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|
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|
11426062 |
Jun 23, 2006 |
7731456 |
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12774951 |
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60725002 |
Oct 7, 2005 |
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Current U.S.
Class: |
406/151 |
Current CPC
Class: |
B05B 12/02 20130101;
B65G 53/525 20130101; B05B 7/1459 20130101; B65G 53/28 20130101;
B05B 12/00 20130101; A01D 87/10 20130101; B05B 7/1454 20130101 |
Class at
Publication: |
406/151 |
International
Class: |
B65G 53/28 20060101
B65G053/28 |
Claims
1. A method of pumping dry particulate material comprising:
applying suction to a volume at time T2, opening an inlet flow path
to the volume at time T3 which is after T2 so that material flows
into the volume under suction, closing the inlet flow path to the
volume, opening an outlet flow path from the volume, and applying
positive pressure to the volume so that material flows out of the
volume.
2. The method of claim 1 wherein the step of applying suction at
time T2 produces and initial higher suction force in the volume
that reduces to a lower suction force before the step of closing
the inlet flow path.
3. The method of claim 1 wherein just prior to time T2 the inlet
flow path and the outlet flow path are closed.
4. The method of claim 1 wherein the step of closing the inlet flow
path begins at time T4 and the inlet flow path is fully closed
before the outlet flow path opens.
5. The method of claim 1 wherein after an initial higher suction
force is applied to the volume at time T2 the suction force reduces
but is a sufficient suction force to suck material into the
volume.
6. The method of claim 5 comprising the step of maintaining
sufficient said suction force as the suction force reduces over
time by monitoring a flow characteristic associated with the
suction force.
7. The method of claim 6 comprising the step of monitoring flow
rate of air out of the volume when suction is applied to the volume
and compensation for decreased flow rate over time by increasing
suction force so as to maintain a predetermined minimum flow
rate.
8. The method of claim 7 comprising the step of adjusting positive
pressure to a venturi pump that is used to produce the suction
force so as to maintain said predetermined minimum flow rate.
9. The method of claim 4 wherein the time period from T2 to T4
occurs about in the middle of a vacuum portion of a pumping cycle,
wherein a pumping cycle includes a pressure portion and a vacuum
portion.
10. A method of pumping powder comprising: applying suction to a
volume to draw material into the volume and applying positive
pressure to push material out of the volume, opening an inlet flow
path at time T3 and closing the inlet flow path at time T4,
applying the positive pressure at time T5, time T5 being after the
time T4 plus a delay for response time has elapsed to ensure the
inlet flow path is fully closed before time T5 occurs.
11. The method of claim 10 wherein the step of closing the inlet
flow path at time T4 comprises applying positive air pressure to a
portion of the inlet flow path to pinch the inlet flow path
closed.
12. A method of pumping powder, comprising: applying suction to a
volume during a suction cycle to draw powder into the volume,
applying positive pressure to the volume to push powder out of the
volume during a delivery cycle, wherein within each suction cycle
is a suction duration period during which suction force is applied
to the volume, the suction duration period being shorter than the
suction cycle and is approximately centered within the suction
cycle.
13. A method of pumping powder, comprising: applying suction to a
volume at time T2, opening an inlet flow path to the volume at time
T3, the time T3 being after the time T2 plus a delay so that when
the inlet flow path is opened an initial higher suction force spike
is applied to draw powder into the volume.
14. A method of pumping powder, comprising: applying suction to a
volume to draw powder into the volume, and controlling the flow
rate of air from the volume during a suction time period.
15. The method of claim 14 wherein the step of controlling the flow
rate of air comprises increasing suction force applied to the
volume over time to maintain a predetermined minimum flow rate.
16. The method of claim 15 comprising the step of monitoring flow
rate by determining pressure drop across an orifice disposed in a
flow path for air sucked from the volume.
Description
RELATED APPLICATIONS
[0001] This application is a divisional of pending U.S. Ser. No.
13/444,321, filed on Apr. 11, 2012, for PUMP FOR POWDER COATING
MATERIALS WITH DATA STRUCTURE FOR STORING POWDER FLOW RECIPES,
which is a continuation of U.S. Ser. No. 12/774,951 filed on May 6,
2010, for PUMP WITH SUCTION AND PRESSURE CONTROL FOR DRY
PARTICULATE MATERIAL, now U.S. Pat. No. 8,167,517, which is a
continuation of U.S. Ser. No. 11/426,062 filed on Jun. 23, 2006,
for PUMP WITH SUCTION AND PRESSURE CONTROL FOR DRY PARTICULATE
MATERIAL, now U.S. Pat. No. 7,731,456, which claims the benefit of
pending U.S. Provisional patent application Ser. No. 60/725,002
filed on Oct. 7, 2005, for DENSE PHASE PUMP IMPROVEMENTS, the
entire disclosures of which are fully incorporated herein by
reference.
TECHNICAL FIELD OF THE INVENTION
[0002] The inventions relate generally to material application and
transfer systems, for example but not limited to powder coating
material application systems. More particularly, the inventions
relate to a pump and pump control functions for such systems.
BACKGROUND OF THE INVENTION
[0003] Material application systems are used to apply one or more
materials in one or more layers to an object. General examples are
powder coating systems, other particulate material application
systems such as may be used in the food processing and chemical
industries. These are but a few examples of a wide and numerous
variety of systems used to apply particulate materials to an
object.
[0004] The application of dry particulate material is especially
challenging on a number of different levels. An example, but by no
means a limitation on the use and application of the present
inventions, is the application of powder coating material to
objects using a powder spray gun. Because sprayed powder tends to
expand into a cloud or diffused spray pattern, known powder
application systems use a spray booth for containment. Powder
particles that do not adhere to the target object are generally
referred to as powder overspray, and these particles tend to fall
randomly within the booth and will alight on almost any exposed
surface within the spray booth. Therefore, cleaning time and color
change times are strongly related to the amount of surface area
that is exposed to powder overspray.
[0005] In addition to surface areas exposed to powder overspray,
color change times and cleaning are strongly related to the amount
of interior surface area exposed to the flow of powder during an
application process. Examples of such interior surface areas
include all surface areas that form the powder flow path, from a
supply of the powder all the way through the powder spray gun. The
powder flow path typically includes a pump that is used to transfer
powder from a powder supply to one or more spray guns. Hoses are
commonly used to connect the pumps to the guns and the supply.
[0006] There are two generally known types of dry particulate
material transfer processes, referred to herein as dilute phase and
dense phase. Dilute phase systems utilize a substantial quantity of
air to push material through one or more hoses or other conduit
from a supply to a spray applicator. A common dilute phase pump
design used in powder coating systems is a venturi pump which
introduces a large volume of air under pressure and higher velocity
into the powder flow. In order to achieve adequate powder flow
rates (in pounds per minute or pounds per hour for example), the
components that make up the flow path must be large enough to
accommodate the flow with such high air to material (in other words
lean flow) otherwise significant back pressure and other
deleterious effects can occur.
[0007] Dense phase systems on the other hand are characterized by a
high material to air ratio (in other words a "rich" flow). A dense
phase pump is described in pending U.S. patent application Ser. No.
10/501,693 filed on Jul. 16, 2004 for PROCESS AND EQUIPMENT FOR THE
CONVEYANCE OF POWDERED MATERIAL, publication WO 05-0095071
published on May 5, 2005, the entire disclosures of which are fully
incorporated herein by reference, and which are owned by the
assignee of the present invention. This pump is characterized in
general by a pump chamber that is partially defined by a gas
permeable member. Material, such as powder coating material as an
example, is drawn into the chamber at one end by gravity and/or
negative pressure and is pushed out of the chamber through an
opposite end by positive air pressure. This pump design is very
effective for transferring material, in part due to the novel
arrangement of a gas permeable member forming part of the pump
chamber. The overall pump, however, in some cases may be less than
optimal for purging, cleaning, color change, maintenance and
material flow rate control.
SUMMARY OF THE INVENTION
[0008] The present disclosure is directed to various improvements
in the pump design set forth in pending U.S. patent application
Ser. No. 10/711,429 filed on Sep. 17, 2004 for DENSE PHASE PUMP FOR
DRY PARTICULATE MATERIAL, publication no. WO 05-0158187 published
on Jul. 21, 2005, the entire disclosures of which are fully
incorporated herein by reference. The present improvements are
generally directed to various control functions relating to
operation of the pump. While the descriptions herein are presented
in the context of a pump in accordance with the referenced
disclosure, those skilled in the art will appreciate that these
improvements may individually or collectively be incorporated into
other pump designs and control functions for different pump
designs, such as for example the Ser. No. 10/501,693 design
referenced herein above.
[0009] In accordance with one inventive aspect, a pump control
function includes applying suction to a volume to draw material
into the volume during a suction time period that is isolated from
a delivery time period during which positive pressure is applied to
push material out of the volume. In a specific embodiment the
suction duration or condition is generally centered within a
suction cycle of the overall pump cycle. In another embodiment, the
suction force initially is at a higher value or spike and then
reduces to a lower value during the suction time duration. In yet
another embodiment, the reduced suction force value is selected to
produce a predetermined air flow rate from the volume during the
suction duration.
[0010] In another inventive aspect, a pump control function
includes applying suction to a volume to draw material into the
volume from an inlet flow path and applying positive pressure to
the volume to push powder out after the inlet flow path is closed.
In a specific embodiment, application of the positive air pressure
is delayed for a period of time to compensate for response time to
close the inlet flow path to ensure that the inlet flow path is
fully closed before the application of positive pressure to the
volume.
[0011] In another inventive aspect, a pump control function
includes controlling the air flow rate from a volume during a
suction time period. In another embodiment, a pump control function
includes controlling the air flow rate into the volume during a
delivery time period. In still another embodiment, a pump control
function includes controlling air flow rate into a volume during a
delivery time period and air flow rate from a volume during a
suction time period. For both types of control functions, in one
embodiment flow rate is monitored by determining pressure drop
across an orifice in the respective air flow path. In yet another
embodiment, a control function includes maintaining predetermined
minimum air flow rates to assure powder is sufficiently sucked in
and pushed out of the volume, and alternatively using either air
flow rate control function individually without the other.
[0012] In another inventive aspect, a pump control function may be
realized with an air flow rate controller for suction, an air flow
rate controller for positive pressure delivery, or both. In a
specific embodiment, either air flow rate control may be effected
by monitoring pressure drop across an orifice in the air flow path
and adjusting a parameter so that the air flow rate is maintained
at a predetermined minimum.
[0013] These and other inventive aspects and advantages of the
present disclosure will be apparent to those skilled in the art
from the following description of the exemplary embodiments in view
of the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a simplified schematic diagram of a powder coating
material application system utilizing the present invention;
[0015] FIGS. 2A-2C are assembled and exploded isometric views of a
pump in accordance with the invention;
[0016] FIGS. 2D-2G are elevation and cross-sectional views of the
assembled pump of FIG. 2A;
[0017] FIGS. 3A and 3B are an isometric and upper plan view of a
pump manifold;
[0018] FIGS. 4A and 4B illustrate a first Y-block;
[0019] FIGS. 5A and 5B are perspective and cross-sectional views of
a valve body;
[0020] FIGS. 6A and 6B illustrate in perspective another Y-block
arrangement;
[0021] FIG. 7 is an exploded perspective of a supply manifold;
[0022] FIG. 8 is an exemplary embodiment of a pneumatic flow
arrangement for the pump of FIG. 2A;
[0023] FIGS. 9A and 9B are an isometric and exploded isometric of a
transfer pump in accordance with the invention;
[0024] FIG. 10 is an exemplary embodiment of a pneumatic flow
arrangement for a transfer pump;
[0025] FIG. 11 is an alternative embodiment of a pneumatic circuit
for the transfer pump;
[0026] FIG. 12 is a representation of material flow rate curves for
a pump operating in accordance with the invention;
[0027] FIG. 13 is a graph depicting powder flow rates versus pinch
valve open duration in milliseconds for two different pump cycle
rates; and
[0028] FIG. 14 is similar to FIG. 2B but labeled differently to
indicate various control elements;
[0029] FIG. 15 illustrates idealized pump cycle timing for a two
chamber pump;
[0030] FIG. 16 illustrates a modified suction cycle for one of the
pump chambers;
[0031] FIG. 17 is a functional diagram of a pneumatic control for a
pump;
[0032] FIG. 18 is an exemplary timing diagram for the control
process represented in FIGS. 16 and 17;
[0033] FIG. 19 is an exemplary timing diagram for a two chamber
pump such as in FIG. 17 to produce a vacuum or suction spike;
[0034] FIG. 20 is a schematic representation of a single pump
chamber control function using a flow rate control feature;
[0035] FIG. 21 is a schematic representation of a single pump
chamber control function using a flow rate control feature on the
positive and negative pressure portions of a pump chamber;
[0036] FIGS. 22A and 22B are a detailed schematic of an overall
pneumatic diagram for a pump control using flow rate controllers
for positive and vacuum pressure control.
DETAILED DESCRIPTION OF THE INVENTION AND EXEMPLARY EMBODIMENTS
THEREOF
[0037] The inventions contemplate a number of new aspects for a
dense phase pump for particulate material. The pump may be used in
combination with any number or type of spray applicator devices or
spray guns and material supply. One or more of the various
inventive aspects or concepts may find application in other pump
designs, such as dilute phase pumps.
[0038] By "dense phase" is meant that the air present in the
particulate flow is about the same as the amount of air used to
fluidize the material at the supply such as a feed hopper. As used
herein, "dense phase" and "high density" are used to convey the
same idea of a low air volume mode of material flow in a pneumatic
conveying system where not all of the material particles are
carried in suspension. In such a dense phase system, the material
is forced along a flow path by significantly less air volume as
compared to a conventional dilute phase system, with the material
flowing more in the nature of plugs that push each other along the
passage, somewhat analogous to pushing the plugs as a piston
through the passage. With smaller cross-sectional passages this
movement can be effected under lower pressures.
[0039] In contrast, conventional flow systems tend to use a dilute
phase which is a mode of material flow in a pneumatic conveying
system where all the particles are carried in suspension.
Conventional flow systems introduce a significant quantity of air
into the flow stream in order to pump the material from a supply
and push it through under positive pressure to the spray
application devices. For example, most conventional powder coating
spray systems utilize venturi pumps to draw fluidized powder from a
supply into the pump. A venturi pump by design adds a significant
amount of air to the powder stream. Typically, flow air and
atomizing air are added to the powder to push the powder under
positive pressure through a feed hose and an applicator device.
Thus, in a conventional powder coating spray system, the powder is
entrained in a high velocity high volume flow of air, thus
necessitating large diameter powder passageways in order to attain
usable powder flow rates.
[0040] Dense phase flow is oftentimes used in connection with the
transfer of material to a closed vessel under high pressure. The
present disclosure, in being directed to material application
rather than simply transport or transfer of material alone,
contemplates flow at substantially lower pressure and flow rates as
compared to dense phase transfer under high pressure to a closed
vessel. However, the disclosure also contemplates a dense phase
transfer pump embodiment which can be used to transfer material to
an open or closed vessel.
[0041] As compared to conventional dilute phase systems having air
volume flow rates of about 3 to about 6 cfm (such as with a venturi
pump arrangement, for example), the present invention may operate
at about 0.8 to about 1.6 cfm, for example. Thus, in the present
invention, powder delivery rates may be on the order of about 150
to about 300 grams per minute. These values are intended to be
exemplary and not limiting. Pumps in accordance with the present
disclosure can be designed to operate at lower or higher air flow
and material delivery values.
[0042] Dense phase versus dilute phase flow can also be thought of
as rich versus lean concentration of material in the air stream,
such that the ratio of material to air is much higher in a dense
phase system. In other words, in a dense phase system the same
amount of material per unit time is transiting a flow path
cross-section (of a tube for example) of lesser area as compared to
a dilute phase flow. For example, in some embodiments herein, the
cross-sectional area of a powder feed tube is about one-fourth the
area of a feed tube for a conventional venturi type system. For
comparable flow of material per unit time then, the material is
about four times denser in the air stream as compared to
conventional dilute phase systems.
[0043] With reference to FIG. 1, in an exemplary embodiment,
various inventive aspects are illustrated being used with a
material application system, such as, for example, a typical powder
coating spray system 10. Such an arrangement commonly includes a
powder spray booth 12 in which an object or part P is to be sprayed
with a powder coating material. The application of powder to the
part P is generally referred to herein as a powder spray, coating
or application operation procedure or process, however, there may
be any number of control functions, steps and parameters that are
controlled and executed before, during and after powder is actually
applied to the part as will be described in greater detail herein
below.
[0044] As is known, the part P is suspended from an overhead
conveyor 14 using hangers 16 or any other conveniently suitable
arrangements. The booth 12 includes one or more openings 18 through
which one or more spray applicators 20 may be used to apply coating
material to the part P as it travels through the booth 12. The
applicators 20 may be of any number depending on the particular
design of the overall system 10. Each applicator can be a manually
operated device as with device 20a, or a system controlled device,
referred to herein as an automatic applicator 20b, wherein the term
"automatic" simply refers to the fact that an automatic applicator
is mounted on a support and is triggered on and off by a control
system, rather than being manually supported and manually
triggered. The present disclosure is directed to manual and
automatic spray applicators.
[0045] It is common in the powder coating material application
industry to refer to the powder applicators as powder spray guns,
and with respect to the exemplary embodiments herein we will use
the terms applicator and gun interchangeably. However, it is
intended that the inventions are useful with material application
devices other than powder spray guns, and hence the more general
term applicator is used to convey the idea that the inventions can
be used in many particulate material application systems other than
the exemplary powder coating material application system described
herein. Some inventive aspects herein are likewise applicable to
electrostatic spray guns as well as non-electrostatic spray guns.
The inventions are also not limited by functionality associated
with the word "spray". Although the inventions are especially
suited to powder spray application, the pump and control concepts
and methods disclosed herein may find use with other material
application techniques beyond just spraying, whether such
techniques are referred to as dispensing, discharge, application or
other terminology that might be used to describe a particular type
of material application device.
[0046] The spray guns 20 receive powder from a supply or feed
center such as a hopper 22 or other material supply through an
associated powder feed or supply hose 24. The automatic guns 20b
typically are mounted on a support 26. The support 26 may be a
simple stationary structure, or may be a movable structure, such as
an oscillator that can move the guns up and down during a spraying
operation, or a gun mover or reciprocator that can move the guns in
and out of the spray booth, or a combination thereof
[0047] The spray booth 12 is designed to contain powder overspray
within the booth, usually by a large flow of containment air into
the booth. This air flow into the booth is usually effected by a
powder overspray reclamation or recovery system 28. The recovery
system 28 pulls air with entrained powder overspray from the booth,
such as for example through a duct 30. In some systems the powder
overspray is returned to the feed center 22 as represented by the
return line 32. In other systems the powder overspray is either
dumped or otherwise reclaimed in a separate receptacle.
[0048] In the exemplary embodiment herein, powder is transferred
from the recovery system 28 back to the feed center 22 by a first
transfer pump 400, an exemplary embodiment of which is described
hereinafter. A respective gun pump 402 is used to supply powder
from the feed center 22 to an associated spray applicator or gun
20. For example, a first gun pump 402a is used to provide dense
phase powder flow to the manual gun 20a and a second gun pump 402b
is used to provide dense phase powder flow to the automatic gun
20b. Exemplary embodiments of the gun pumps 402 are described
hereinafter.
[0049] Each gun pump 402 operates from pressurized gas such as
ordinary air supplied to the gun by a pneumatic supply manifold
404. One inventive aspect provides a pump and manifold arrangement
by which the pump 402 is mounted to the supply manifold 404 with a
gasket or other seal device therebetween. This eliminates
unnecessary plumbing between the manifold 404 and the pump 402.
Although schematically illustrated in FIG. 1 as being directly
joined, it is contemplated that in practice the manifolds 404 will
be disposed in a cabinet or other enclosure and mounted to the
pumps 402 with a wall of the cabinet therebetween. In this manner,
the manifolds 404, which may include electrical power such as
solenoid valves, are isolated from the spraying environment. The
pump design also allows the pump to be positioned outside of the
spraying environment in contrast to conventional venturi pumps.
[0050] The supply manifold 404 supplies pressurized air to its
associated pump 402 for purposes that will be explained
hereinafter. In addition, each supply manifold 404 includes a
pressurized pattern air supply that is provided to the spray guns
20 via air hoses or lines 405. Main air 408 is provided to the
supply manifold 404 from any convenient source within the
manufacturing facility of the end user of the system 10. Each pump
402 supplies powder to its respective applicator 20 via a powder
supply hose 406.
[0051] In the FIG. 1 embodiment, a second transfer pump 410 is used
to transfer powder from a supply 412 of virgin powder (that is to
say, unused) to the feed center 22. Those skilled in the art will
understand that the number of required transfer pumps 410 and gun
pumps 402 will be determined by the requirements of the overall
system 10 as well as the spraying operations to be performed using
the system 10.
[0052] Although the gun pump and the transfer pumps may be the same
design, in the exemplary embodiments there are differences that
will be described hereinafter. Those differences take into account
that the gun pump preferably provides a smooth consistent flow of
powder material to the spray applicators 20 in order to provide the
best coating onto the objects P, whereas the transfer pumps 400 and
410 are simply used to move powder from one receptacle to another
at a high enough flow rate and volume to keep up with the powder
demand from the applicators and as optionally supplemented by the
powder overspray collected by the recovery system 28.
[0053] Other than the pumps 400, 410 and 402, the selected design
and operation of the material application system 10, including the
spray booth 12, the conveyor 14, the guns 20, the recovery system
28, and the feed center or supply 22, form no necessary part of the
present invention and may be selected based on the requirements of
a particular coating application. A particular spray applicator,
however, that is well suited for use with the present inventions is
described in pending International patent application number
PCT/US04/26887 for SPRAY APPLICATOR FOR PARTICULATE MATERIAL, filed
on Aug. 18, 2004, the entire disclosure of which is incorporated
herein by reference. However, many other applicator designs may be
used as required for a particular application. A control system 39
likewise may be a conventional control system such as a
programmable processor based system or other suitable control
circuit. The control system 39 executes a wide variety of control
functions and algorithms, typically through the use of programmable
logic and program routines, which are generally indicated in FIG. 1
as including but not necessarily limited to feed center control 36
(for example supply controls and pump operation controls), gun
operation control 38 (such as for example, gun trigger controls),
gun position control 40 (such as for example control functions for
the reciprocator/gun mover 26 when used), powder recovery system
control 42 (for example, control functions for cyclone separators,
after filter blowers and so on), conveyor control 44 and material
application parameter controls 46 (such as for example, powder flow
rates, applied film thickness, electrostatic or non-electrostatic
application and so on). Conventional control system theory, design
and programming may be utilized. The present disclosure, however,
provides a number of inventive aspects and concepts relating to the
control functions executed by the control system 39 as will be
further described herein.
[0054] While the described embodiments herein are presented in the
context of a dense phase pump for use in a powder coating material
application system, those skilled in the art will readily
appreciate that the present inventions may be used in many
different dry particulate material application systems, including
but not limited in any manner to: talc on tires, super-absorbents
such as for diapers, food related material such as flour, sugar,
salt and so on, desiccants, release agents, and pharmaceuticals.
These examples are intended to illustrate the broad application of
the inventions for dense phase application of particulate material
to objects. The specific design and operation of the material
application system selected provides no limitation on the present
inventions except as otherwise expressly noted herein. Various
inventive aspects and concepts herein may also find use in dilute
phase systems.
[0055] While various inventive aspects, concepts and features of
the inventions may be described and illustrated herein as embodied
in combination in the exemplary embodiments, these various aspects,
concepts and features may be used in many alternative embodiments,
either individually or in various combinations and sub-combinations
thereof Unless expressly excluded herein all such combinations and
sun-combinations are intended to be within the scope of the present
inventions. Still further, while various alternative embodiments as
to the various aspects, concepts and features of the
inventions--such as alternative materials, structures,
configurations, methods, circuits, devices and components,
software, hardware, control logic, alternatives as to form, fit and
function, and so on--may be described herein, such descriptions are
not intended to be a complete or exhaustive list of available
alternative embodiments, whether presently known or later
developed. Those skilled in the art may readily adopt one or more
of the inventive aspects, concepts or features into additional
embodiments and uses within the scope of the present inventions
even if such embodiments are not expressly disclosed herein.
Additionally, even though some features, concepts or aspects of the
inventions may be described herein as being a preferred arrangement
or method, such description is not intended to suggest that such
feature is required or necessary unless expressly so stated. Still
further, exemplary or representative values and ranges may be
included to assist in understanding the present disclosure,
however, such values and ranges are not to be construed in a
limiting sense and are intended to be critical values or ranges
only if so expressly stated. Moreover, while various aspects,
features and concepts may be expressly identified herein as being
inventive or forming part of an invention, such identification is
not intended to be exclusive, but rather there may be inventive
aspects, concepts and features that are fully described herein
without being expressly identified as such or as part of a specific
invention, the inventions instead being set forth in the appended
claims. Descriptions of exemplary methods or processes are not
limited to inclusion of all steps as being required in all cases,
nor is the order that the steps are presented to be construed as
required or necessary unless expressly so stated.
[0056] Even from the general schematic illustration of FIG. 1 it
can be appreciated that such complex systems can be very difficult
and time consuming to clean and to provide for color change.
Typical powder coating material is a very fine particulate and
tends to be applied in a fine cloud or spray pattern directed at
the objects being sprayed. Even with the use of electrostatic
technology, a significant amount of powder overspray is inevitable.
Cross contamination during color change is a significant issue in
many industries, therefore it is important that the material
application system be able to be thoroughly cleaned between color
changes. Color changes however necessitate taking the material
application system offline and thus is a significant cost driver.
The present inventions are directed in part to providing a pump
that is easier and faster to clean. Additional inventive features
and aspects are applicable separately from the concern for
cleanability and color change times.
[0057] With reference to FIGS. 2A, 2B and 2C there is illustrated
an exemplary embodiment of a dense phase pump 402. Although the
pump 402 can be used as a transfer pump as well, it is particularly
designed as a gun pump for supplying material to the spray
applicators 20. The gun pumps 402 and transfer pumps 400 and 410
share many common design features which will be readily apparent
from the detailed descriptions herein.
[0058] In accordance with one inventive aspect, the pump 402 is
preferably although need not be modular in design. The modular
construction of the pump 402 is realized with a pump manifold body
414 and a valve body 416. The manifold body 414 houses a pair of
pump chambers along with a number of air passages as will be
further explained herein. The valve body 416 houses a plurality of
valve elements as will also be explained herein. The valves respond
to air pressure signals that are communicated into the valve body
416 from the manifold body 414. Although the exemplary embodiments
herein illustrate the use of pneumatic pinch valves, those skilled
in the are will readily appreciate that various aspects and
advantages of the present inventions may be realized with the use
of other control valve designs other than pneumatic pinch
valves.
[0059] The upper portion 402a of the pump is adapted for purge air
arrangements 418a and 418b, and the lower portion 402b of the pump
is adapted for a powder inlet hose connector 420 and a powder
outlet hose connector 422. A powder feed hose 24 (FIG. 1) is
connected to the inlet connector 420 to supply a flow of powder
from a supply such as the feed hopper 22. A powder supply hose 406
(FIG. 1) is used to connect the outlet 422 to a spray applicator
whether it be a manual or automatic spray gun positioned up at the
spray booth 12. The powder supplied to the pump 402 may, but not
necessarily must, be fluidized.
[0060] Powder flow into an out of the pump 402 thus occurs on a
single end 402b of the pump. This allows a purge function 418 to be
provided at the opposite end 402a of the pump thus providing an
easier purging operation as will be further explained herein.
[0061] If there were only one pump chamber (which is a useable
alternative embodiment) then the valve body 416 could be directly
connected to the manifold because there would only be the need for
two powder paths through the pump. However, in order to produce a
steady, consistent and adjustable flow of powder from the pump, two
or more pump chambers are provided. When two pump chambers are
used, they are preferably operated out of phase so that as one
chamber is receiving powder from the inlet the other is supplying
powder to the outlet. In this way, powder flows substantially
continuously from the pump. With a single chamber this would not be
the case because there is a gap in the powder flow from each
individual pump chamber due to the need to first fill the pump
chamber with powder. When more than two chambers are used, their
timing can be adjusted as needed. In any case it is preferred
though not required that all pump chambers communicate with a
single inlet and a single outlet.
[0062] In accordance with one inventive aspect, material flow into
and out of each of the pump chambers is accomplished at a single
end of the chamber. This provides an arrangement by which a
straight through purge function can be used at an opposite end of
the pump chamber. Since each pump chamber communicates with the
same pump inlet and outlet in the exemplary embodiment, additional
modular units are used to provide branched powder flow paths in the
form of Y blocks.
[0063] A first Y-block 424 is interconnected between the manifold
body 414 and the valve body 416. A second Y-block 426 forms the
inlet/outlet end of the pump and is connected to the side of the
valve body 416 that is opposite the first Y-block 424. A first set
of bolts 428 are used to join the manifold body 414, first Y-block
424 and the valve body 416 together. A second set of bolts 430 are
used to join the second Y-block 426 to the valve body 416. Thus the
pump in FIG. 2A when fully assembled is very compact and sturdy,
yet the lower Y-block 426 can easily and separately be removed for
replacement of flow path wear parts without complete disassembly of
the pump. The first Y-block 424 provides a two branch powder flow
path away from each powder chamber. One branch from each chamber
communicates with the pump inlet 420 through the valve body 416 and
the other branch from each chamber communicates with the pump
outlet 422 through the valve body 416. The second Y-block 426 is
used to combine the common powder flow paths from the valve body
416 to the inlet 420 and outlet 422 of the pump. In this manner,
each pump chamber communicates with the pump inlet through a
control valve and with the pump outlet through another control
valve. Thus, in the exemplary embodiment, there are four control
valves in the valve body that control flow of powder into and out
of the pump chambers.
[0064] The manifold body 414 is shown in detail in FIGS. 2B, 2E,
2G, 3A and 3B. The manifold 414 includes a body 432 having first
and second bores therethrough 434, 436 respectively. Each of the
bores receives a generally cylindrical gas permeable filter member
438 and 440 respectively. The gas permeable filter members 438, 440
include lower reduced outside diameter ends 438a and 440a which
insert into a counterbore inside the first Y-block 424 (FIG. 4B)
which helps to maintain the members 438, 440 aligned and stable.
The upper ends of the filter members abut the bottom ends of purge
air fittings 504 with appropriate seals as required. The filter
members 438, 440 each define an interior volume (438c, 440c) that
serves as a powder pump chamber so that there are two pump powder
chambers provided in this embodiment. A portion of the bores 434,
436 are adapted to receive the purge air arrangements 418a and 418b
as will be described hereinafter.
[0065] The filter members 438, 440 may be identical and allow a
gas, such as ordinary air, to pass through the cylindrical wall of
the member but not powder. The filter members 438, 440 may be made
of porous polyethylene, for example. This material is commonly used
for fluidizing plates in powder feed hoppers. An exemplary material
has about a 40 micron opening size and about a 40-50% porosity.
Such material is commercially available from Genpore or Poron.
Other porous materials may be used as needed. The filter members
438, 440 each have a diameter that is less than the diameter of its
associated bore 434, 436 so that a small annular space is provided
between the wall of the bore and the wall of the filter member (see
FIGS. 2E, 2G). This annular space serves as a pneumatic pressure
chamber. When a pressure chamber has negative pressure applied to
it, powder is drawn up into the powder pump chamber and when
positive pressure is applied to the pressure chamber the powder in
the powder pump chamber is forced out.
[0066] The manifold body 432 includes a series of six inlet
orifices 442. These orifices 442 are used to input pneumatic energy
or signals into the pump. Four of the orifices 442a, c, d and f are
in fluid communication via respective air passages 444a, c, d and f
with a respective pressure chamber 446 in the valve block 416 and
thus are used to provide valve actuation air as will be explained
hereinafter. Note that the air passages 444 extend horizontally
from the manifold surface 448 into the manifold body and then
extend vertically downward to the bottom surface of the manifold
body where they communicate with respective vertical air passages
through the upper Y-block 424 and the valve body 416 wherein they
join to respective horizontal air passages in the valve body 416 to
open into each respective valve pressure chamber. Air filters (not
shown) may be included in these air passages to prevent powder from
flowing up into the pump manifold 414 and the supply manifold 404
in the event that a valve element or other seal should become
compromised. The remaining two orifices, 442b and 442e are
respectively in fluid communication with the bores 434, 436 via air
passages 444b and 444e. These orifices 442b and 442e are thus used
to provide positive and negative pressure to the pump pressure
chambers in the manifold body.
[0067] The orifices 442 are preferably, although need not be,
formed in a single planar surface 448 of the manifold body. The air
supply manifold 404 includes a corresponding set of orifices that
align with the pump orifices 442 and are in fluid communication
therewith when the supply manifold 404 is mounted on the pump
manifold 414. In this manner the supply manifold 404 can supply all
required pump air for the valves and pump chambers through a simple
planar interface. A seal gasket 450 is compressed between the faces
of the pump manifold 414 and the supply manifold 404 to provide
fluid tight seals between the orifices. Because of the volume,
pressure and velocity desired for purge air, preferably separate
purge air connections are used between the supply manifold and the
pump manifold. Although the planar interface between the two
manifolds is preferred it is not required, and individual
connections for each pneumatic input to the pump from the supply
manifold 404 could be used as required. The planar interface allows
for the supply manifold 404, which in some embodiments includes
electrical solenoids, to be placed inside a cabinet with the pump
on the outside of the cabinet (mounted to the supply manifold
through an opening in a cabinet wall) so as to help isolate
electrical energy from the overall system 10. It is noted in
passing that the pump 402 need not be mounted in any particular
orientation during use.
[0068] With reference to FIGS. 4A and 4B, the first Y-block 424
includes first and second ports 452, 454 that align with their
respective pump chamber 434, 436. Each of the ports 452, 454
communicates with two branches 452a, 452b and 454a, 454b
respectively (FIG. 4B only shows the branches for the port 452).
Thus, the port 452 communicates with branches 452a and 452b.
Therefore, there are a total of four branches in the first Y-block
424 wherein two of the branches communicate with one pressure
chamber and the other two communicate with the other pressure
chamber. The branches 452a, b and 454a, b form part of the powder
path through the pump for the two pump chambers. Flow of powder
through each of the four branches is controlled by a separate pinch
valve in the valve body 416 as will be described herein. Note that
the Y-block 424 also includes four through air passages 456a, c, d,
f which are in fluid communication with the air passages 444a, c, d
and f respectively in the manifold body 414. A gasket 459 may be
used to provide fluid tight connection between the manifold body
414 and the first Y-block 424.
[0069] The ports 452 and 454 include counterbores 458, 460 which
receive seals 462, 464 (FIG. 2C) such as conventional o-rings.
These seals provide a fluid tight seal between the lower ends of
the filter members 438, 440 and the Y-block ports 452, 454. They
also allow for slight tolerance variations so that the filter
members are tightly held in place.
[0070] With additional reference to FIGS. 5A and 5B, the valve body
416 includes four through bores 446a, 446b, 446c and 446d that
function as pressure chambers for a corresponding number of pinch
valves. The upper surface 466 of the valve body includes two
recessed regions 468 and 470 each of which includes two ports, each
port being formed by one end of a respective bore 446. In this
embodiment, the first recessed portion 468 includes orifices 472
and 474 which are formed by their respective bores 446b and 446a
respectively. Likewise, the second recessed portion 470 includes
orifices 476 and 478 which are formed by their respective bores
446d and 446c respectively. Corresponding orifices are formed on
the opposite side face 479 of the valve body 416.
[0071] Each of the pressure chambers 446a-d retains either an inlet
pinch valve element 480 or an outlet pinch valve 481. Each pinch
valve element 480, 481 is a fairly soft flexible member made of a
suitable material, such as for example, natural rubber, latex or
silicone. Each valve element 480, 481 includes a central generally
cylindrical body 482 and two flanged ends 484 of a wider diameter
than the central body 482. The flanged ends function as seals and
are compressed about the bores 446a-d when the valve body 416 is
sandwiched between the first Y-block 424 and the second Y-block
426. In this manner, each pinch valve defines a flow path for
powder through the valve body 416 to a respective one of the
branches 452, 454 in the first Y-block 424. Therefore, one pair of
pinch valves (a suction valve and a delivery valve) communicates
with one of the pump chambers 440 in the manifold body while the
other pair of pinch valves communicates with the other pump chamber
438. There are two pinch valves per chamber because one pinch valve
controls the flow of powder into the pump chamber (suction) and the
other pinch valve controls the flow of powder out of the pump
chamber (delivery). The outer diameter of each pinch valve central
body portion 482 is less than the bore diameter of its respect
pressure chamber 446. This leaves an annular space surrounding each
pinch valve that functions as the pressure chamber for that
valve.
[0072] The valve body 416 includes air passages 486a-d that
communicate respectively with the four pressure chamber bores
446a-d. as illustrated in FIG. 5B. These air passages 486a-d
include vertical extensions (as viewed in FIG. 5B) 488a-d. These
four air passage extensions 488a, b, c, d respectively are in fluid
communication with the vertical portions of the four air passages
444d, f, a, c in the manifold 414 and the vertical passages 456d,
f, a, c in the upper Y-block 424. Seals 490 are provided for air
tight connections.
[0073] In this manner, each of the pressure chambers 446 in the
valve body 416 is in fluid communication with a respective one of
the air orifices 442 in the manifold body 414, all through internal
passages through the manifold body, the first Y-block and the valve
body. When positive air pressure is received from the supply
manifold 404 (FIG. 1) into the pump manifold 414, the corresponding
valve 480, 481 is closed by the force of the air pressure acting
against the outer flexible surface of the flexible valve body. The
valves open due to their own resilience and elasticity when
external air pressure in the pressure chamber is removed. This true
pneumatic actuation avoids any mechanical actuation or other
control member being used to open and close the pinch valves which
is a significant improvement over the conventional designs. Each of
the four pinch valves 480, 481 is preferably separately controlled
for the gun pump 402.
[0074] In accordance with another aspect of the inventions, the
valve body 416 is preferably made of a sufficiently transparent
material so that an operator can visually observe the opening and
closing of the pinch valves therein. A suitable material is acrylic
but other transparent materials may be used. The ability to view
the pinch valves also gives a good visual indication of a pinch
valve failure since powder will be visible.
[0075] With additional reference to FIGS. 6A and 6B, the remaining
part of the pump is the inlet end 402b formed by a second Y-block
end body 492. The end body 492 includes first and second recesses
494, 496 each of which is adapted to receive a Y-block 498a and
498b. One of the Y-blocks is used for powder inlet and the other is
used for powder outlet. Each Y-block 498 is a wear component due to
exposure of its internal surfaces to powder flow. Since the body
492 is simply bolted to the valve body 416, it is a simple matter
to replace the wear parts by removing the body 492, thus avoiding
having to disassemble the rest of the pump.
[0076] Each Y-block 498 includes a lower port 500 that is adapted
to receive a fitting or other suitable hose connector 420, 422
(FIG. 2A) with one fitting connected to a hose 24 that runs to a
powder supply and another hose 406 to a spray applicator such as a
spray gun 20 (FIG. 1). Each Y-block includes two powder path
branches 502a, 502b, 502c and 502d that extend away from the port
500. Each powder path in the second Y-blocks 498 are in fluid
communication with a respective one of the pinch valves 480, 481 in
the pinch valve body 416. Thus, powder that enters the pump at the
inlet 420 branches through a first of the two lower Y-blocks 498
into two of the pinch valves and from there to the pump chambers.
Likewise powder from the two pump chambers recombine from the other
two pinch valves into a single outlet 422 by way of the other lower
Y-block 498.
[0077] The powder flow paths are as follows. Powder enters through
a common inlet 420 and branches via paths 502a or 502b in the lower
Y-block 498b to the two inlet or suction pinch valves 480. Each of
the inlet pinch valves 480 is connected to a respective one of the
powder pump chambers 434, 436 via a respective one branch 452, 454
of a respective path through the first or upper Y-block 424. Each
of the other branches 452, 454 of the upper Y-block 424 receive
powder from a respective pump chamber, with the powder flowing
through the first Y-block 424 to the two outlet or delivery pinch
valves 481. Each of the outlet pinch valves 481 is also connected
to a respect one of the branches 502 in the lower Y-block 498a
wherein the powder from both pump chambers is recombined to the
single outlet 422.
[0078] The pneumatic flow paths are as follows. When any of the
pinch valves is to be closed, the supply manifold 404 issues a
pressure increase at the respective orifice 442 in the manifold
body 414. The increased air pressure flows through the respective
air passage 442, 444 in the manifold body 414, down through the
respective air passage 456 in the first Y-block 424 and into the
respective air passage 486 in the valve body 416 to the appropriate
pressure chamber 446.
[0079] It should be noted that a pump in accordance with the
present inventions provides for a proportional flow valve based on
percent fill of the powder pump chambers, meaning that the flow
rate of powder from the pump can be accurately controlled by
controlling the open time of the pinch valves that feed powder to
the pump chambers. This allows the pump cycle (i.e. the total time
duration for filling and emptying the pump chambers) to be short
enough so that a smooth flow of powder is achieved independent of
the flow rate, with the flow rate being separately controlled by
operation of the pinch valves. Thus, flow rate can be adjusted
entirely by control of the pinch valves without having to make any
physical changes to the pump.
[0080] The purge function is greatly simplified in accordance with
another inventive aspect. Because the pump design provides a way
for powder to enter and exit the pump chambers from a single end,
the opposite end of the pump chamber can be used for purge air.
With reference to FIGS. 2A, 2C, 2E and 2G, a purge air fitting 504
is inserted into the upper end of its respective pump chamber 438,
440. The fittings 504 receive respective check valves 506 that are
arranged to only permit flow into the pump chambers 438, 440. The
check valves 506 receive respective purge air hose fittings 508 to
which a purge air hose can be connected. Purge air is supplied to
the pump from the supply manifold 404 as will be described
hereinbelow. The purge air thus can flow straight through the
powder pump chambers and through the rest of the powder path inside
the pump to very effectively purge the pump for a color change
operation. No special connections or changes need to be made by the
operator to effect this purging operation, thereby reducing
cleaning time. Once the system 10 is installed, the purging
function is always connected and available, thereby significantly
reducing color change time because the purging function can be
executed by the control system 39 without the operator having to
make or break any powder or pneumatic connections with the
pump.
[0081] Note from FIGS. 1 and 2A that with all four pinch valves
480, 481 in an open condition purge air will flow straight through
the pump chambers, through the powder paths in the first Y-block
424, the pinch valves themselves 480, 481, the second Y-block 498
and out both the inlet 420 and the outlet 422. Purge air thus can
be supplied throughout the pump and then on to the spray applicator
to purge that device as well as to purge the feed hoses back to the
powder supply 22. Thus in accordance with another inventive aspect,
a dense phase pump concept is provided that allows forward and
reverse purging.
[0082] With reference to FIG. 7, the supply manifold 404
illustrated is in essence a series of solenoid valves and air
sources that control the flow of air to the pump 402. The
particular arrangement illustrated in FIG. 7 is exemplary and not
intended to be limiting. The supply of air to operate the pump 402
can be done without a manifold arrangement and in a wide variety of
ways. The embodiment of FIG. 7 is provided as it is particularly
useful for the planar interface arrangement with the pump, however,
other manifold designs can also be used.
[0083] The supply manifold 404 includes a supply manifold body 510
that has a first planar face 512 that is mounted against the
surface 448 of the pump manifold body 414 (FIG. 3A) as previously
described herein. Thus the face 512 includes six orifices 514 that
align with their respective orifices 442 in the pump manifold 414.
The supply manifold body 510 is machined to have the appropriate
number and location of air passages therein so that the proper air
signals are delivered to the orifices 514 at the correct times. As
such, the manifold further includes a series of valves that are
used to control the flow of air to the orifices 514 as well as to
control the purge air flow. Negative pressure is generated in the
manifold 404 by use of a conventional venturi pump 518. System or
shop air is provided to the manifold 404 via appropriate fittings
520. The details of the physical manifold arrangement are not
necessary to understand and practice the present inventions since
the manifold simply operates to provide air passages for air
sources to operate the pump and can be implemented in a wide
variety of ways. Rather, the details of note are described in the
context of a schematic diagram of the pneumatic flow. It is noted
at this time, however, that in accordance with another inventive
aspect, a separate control valve is provided for each of the pinch
valves in the valve body 414 for purposes that will be described
hereinafter.
[0084] With reference to FIG. 8, a pneumatic diagram is provided
for a first embodiment of one aspect of the invention. Main air 408
enters the supply manifold 404 and goes to a first regulator 532 to
provide pump pressure source 534 to the pump chambers 438, 440, as
well as pattern shaping air source 405 to the spray applicator 20
via air hose 406. Main air also is used as purge air source 536
under control of a purge air solenoid valve 538. Main air also goes
to a second regulator 540 to produce venturi air pressure source
542 used to operate the venturi pump (to produce the negative
pressure to the pump chambers 438, 440) and also to produce pinch
air source 544 to operate the pinch valves 480, 481.
[0085] In accordance with another aspect of the invention, the use
of the solenoid control valve 538 or other suitable control device
for the purge air provides multiple purge capability. The first
aspect is that two or more different purge air pressures and flows
can be selected, thus allowing a soft and hard purge function.
Other control arrangements besides a solenoid valve can be used to
provide two or more purge air flow characteristics. The control
system 39 selects soft or hard purge, or a manual input could be
used for this selection. For a soft purge function, a lower purge
air flow is supplied through the supply manifold 404 into the pump
pressure chambers 434, 436 which is the annular space between the
porous members 438, 440 and their respective bores 434, 436. The
control system 39 further selects one set of pinch valves (suction
or delivery) to open while the other set is closed. The purge air
bleeds through the porous filters 438, 440 and out the open valves
to either purge the system forward to the spray gun 20 or reverse
(backward) to the supply 22. The control system 39 then reverses
which pinch valves are open and closed. Soft purge may also be done
in both directions at the same time by opening all four pinch
valves. Similarly, higher purge air pressure and flow may be used
for a hard purge function forward, reverse or at the same time. The
purge function carried out by bleeding air through the porous
members 438, 440 also helps to remove powder that has been trapped
by the porous members, thus extending the useful life of the porous
members before they need to be replaced.
[0086] Hard or system purge can also be effected using the two
purge arrangements 418a and 418b. High pressure flow air can be
input through the purge air fittings 508 (the purge air can be
provided from the supply manifold 404) and this air flows straight
through the powder pump chambers defined in part by the porous
members 438, 440 and out the pump. Again, the pinch valves 480, 481
can be selectively operated as desired to purge forward or reverse
or at the same time.
[0087] It should be noted that the ability to optionally purge in
only the forward or reverse direction provides a better purging
capability because if purging can only be done in both directions
at the same time, the purge air will flow through the path of least
resistance whereby some of the powder path regions may not get
adequately purged. For example, when trying the purge a spray
applicator and a supply hopper, if the applicator is completely
open to air flow, the purge air will tend to flow out the
applicator and might not adequately purge the hopper or supply.
[0088] The present disclosure thus provides a pump design by which
the entire powder path from the supply to and through the spray
guns can be purged separately or at the same time with virtually no
operator action required. The optional soft purge may be useful to
gently blow out residue powder from the flow path before hitting
the powder path with hard purge air, thereby preventing impact
fusion or other deleterious effects from a hard purge being
performed first.
[0089] The positive air pressure 542 for the venturi enters a
control solenoid valve 546 and from there goes to the venturi pump
518. The output 518a of the venturi pump is a negative pressure or
partial vacuum that is connected to an inlet of two pump solenoid
valves 548, 550. The pump valves 548 and 550 are used to control
whether positive or negative pressure is applied to the pump
chambers 438, 440. Additional inputs of the valves 548, 550 receive
positive pressure air from a first servo valve 552 that receives
pump pressure air 534. The outlets of the pump valves 548, 550 are
connected to a respective one of the pump chambers through the air
passage scheme described hereinabove. Note that the purge air 536
is schematically indicated as passing through the porous tubes 438,
440.
[0090] Thus, the pump valves 550 and 548 are used to control
operation of the pump 402 by alternately applying positive and
negative pressure to the pump chambers, typically 180.degree. out
of phase so that as one chamber is being pressurized the other is
under negative pressure and vice-versa. In this manner, one chamber
is filling with powder while the other chamber is emptying. It
should be noted that the pump chambers may or may not completely
"fill" with powder. As will be explained herein, very low powder
flow rates can be accurately controlled using the present invention
by use of the independent control valves for the pinch valves. That
is, the pinch valves can be independently controlled apart from the
cycle rate of the pump chambers to feed more or less powder into
the chambers during each pumping cycle.
[0091] Pinch valve air 544 is input to four pinch valve control
solenoids 554, 556, 558 and 560. Four valves are used so that there
is preferably independent timing control of the operation of each
of the four pinch valves 480, 481. In FIG. 8, "delivery pinch
valve" refers to those two pinch valves 481 through which powder
exits the pump chambers and "suction pinch valve" refers to those
two pinch valves 480 through which powder is fed to the pump
chambers. Though the same reference numeral is used, each suction
pinch valve and each delivery pinch valve is separately
controlled.
[0092] A first delivery solenoid valve 554 controls air pressure to
a first delivery pinch valve 481; a second delivery solenoid valve
558 controls air pressure to a second delivery pinch valve 481; a
first suction solenoid valve 556 controls air pressure to a first
suction pinch valve 480 and a second suction solenoid valve 560
controls air pressure to a second suction pinch valve 480.
[0093] The pneumatic diagram of FIG. 8 thus illustrates the
functional air flow that the manifold 404 produces in response to
various control signals from the control system 39 (FIG. 1).
[0094] With reference to FIGS. 9A and 9B, and in accordance with
another inventive aspect, a transfer pump 400 is also contemplated.
Many aspects of the transfer pump are the same or similar to the
spray applicator pump 402 and therefore need not be repeated in
detail.
[0095] Although a gun pump 402 may be used as a transfer pump as
well, a transfer pump is primarily used for moving larger amounts
of powder between receptacles as quickly as needed. Moreover,
although a transfer pump as described herein will not have the same
four way independent pinch valve operation, a transfer valve may be
operated with the same control process as the gun pump. For
example, some applications require large amounts of material to be
applied over large surfaces yet maintaining control of the finish.
A transfer pump could be used as a pump for the applicators by also
incorporating the four independent pinch valve control process
described herein.
[0096] In the system of FIG. 1 a transfer pump 400 is used to move
powder from the recovery system 28 (such as a cyclone) back to the
feed center 22. A transfer pump 410 is also used to transfer virgin
powder from a supply, such as a box, to the feed center 22. In such
examples as well as others, the flow characteristics are not as
important in a transfer pump because the powder flow is not being
sent to a spray applicator. In accordance then with an aspect of
the invention, the gun pump is modified to accommodate the
performance expectations for a transfer pump.
[0097] In the transfer pump 400, to increase the powder flow rate
larger pump chambers are needed. In the embodiment of FIGS. 9A and
9B, the pump manifold is now replaced with two extended tubular
housings 564 and 566 which enclose lengthened porous tubes 568 and
570. The longer tubes 568, 570 can accommodate a greater amount of
powder during each pump cycle. The porous tubes 568, 570 have a
slightly smaller diameter than the housings 564, 566 so that an
annular space is provided therebetween that serves as a pressure
chamber for both positive and negative pressure. Air hose fittings
572 and 574 are provided to connect air hoses that are also
connected to a source of positive and negative pressure at a
transfer pump air supply system to be described hereinafter. Since
a pump manifold is not being used, the pneumatic energy is
individually plumbed into the pump 400.
[0098] The air hose fittings 572 and 574 are in fluid communication
with the pressure chambers within the respective housings 564 and
566. In this manner, powder is drawn into and pushed out of the
powder chambers 568, 570 by negative and positive pressure as in
the gun pump design. Also similarly, purge port arrangements 576
and 578 are provided and function the same way as in the gun pump
design, including check valves 580, 582.
[0099] A valve body 584 is provided that houses four pinch valves
585 which control the flow of powder into and out of the pump
chambers 568 and 570 as in the gun pump design. As in the gun pump,
the pinch valves are disposed in respective pressure chambers in
the valve body 584 such that positive air pressure is used to close
a valve and the valves open under their own resilience when the
positive pressure is removed. A different pinch valve actuation
scheme however is used as will be described shortly. An upper
Y-block 586 and a lower Y-block 588 are also provided to provide
branched powder flow paths as in the gun pump design. The lower
Y-block 588 thus is also in communication with a powder inlet
fitting 590 and a powder outlet fitting 592. Thus, powder in from
the single inlet flows to both pump chambers 568, 570 through
respective pinch valves and the upper Y-block 586, and powder out
of the pump chambers 568, 570 flows through respective pinch valves
to the single outlet 592. The branched powder flow paths are
realized in a manner similar to the gun pump embodiment and need
not be repeated herein. The transfer pump may also incorporate
replaceable wear parts or inserts in the lower Y-block 588 as in
the gun pump.
[0100] Again, since a pump manifold is not being used in the
transfer pump, separate air inlets 594 and 596 are provided for
operation of the pinch valves which are disposed in pressure
chambers as in the gun pump design. Only two air inlets are needed
even though there are four pinch valves for reasons set forth
below. An end cap 598 may be used to hold the housings in alignment
and provide a structure for the air fittings and purge
fittings.
[0101] Because quantity of flow is of greater interest in the
transfer pump than quality of the powder flow, individual control
of all four pinch valves is not needed although it could
alternatively be done. As such, pairs of the pinch valves can be
actuated at the same time, coincident with the pump cycle rate. In
other words, when the one pump chamber is filling with powder, the
other is discharging powder, and respective pairs of the pinch
valves are thus open and closed. The pinch valves can be actuated
synchronously with actuation of positive and negative pressure to
the pump chambers. Moreover, single air inlets to the pinch valve
pressure chambers can be used by internally connecting respective
pairs of the pressure chambers for the pinch valve pairs that
operate together. Thus, two pinch valves are used as delivery
valves for powder leaving the pump, and two pinch valves are used
as suction valves for powder being drawing into the pump. However,
because the pump chambers alternate delivery and suction, during
each half cycle there is one suction pinch valve open and one
delivery pinch valve open, each connected to different ones of the
pump chambers. Therefore, internally the valve body 584 the
pressure chamber of one of the suction pinch valves and the
pressure chamber for one of the delivery pinch valves are connected
together, and the pressure chambers of the other two pinch valves
are also connected together. This is done for pinch valve pairs in
which each pinch valve is connected to a different pump chamber.
The interconnection can be accomplished by simply providing
cross-passages within the valve body between the pair of pressure
chambers.
[0102] With reference to FIG. 10, the exemplary pneumatic diagram
for the transfer pump 400 is somewhat more simplified than for a
pump that is used with a spray applicator. Main air 408 is input to
a venturi pump 600 that is used to produce negative pressure for
the transfer pump chambers. Main air also is input to a regulator
602 with delivery air being supplied to respective inputs to first
and second chamber solenoid valves 604, 606. The chamber valves
also receive as an input the negative pressure from the venturi
pump 600. The solenoid valves 604, 606 have respective outputs 608,
610 that are in fluid communication with the respective pressure
chambers of the transfer pump.
[0103] The solenoid valves in this embodiment are air actuated
rather than electrically actuated. Thus, air signals 612 and 614
from a pneumatic timer or shuttle valve 616 are used to alternate
the valves 604, 606 between positive and negative pressure outputs
to the pressure chambers of the pump. An example of a suitable
pneumatic timer or shuttle valve is model S9 568/68-1/4-SO
available from Hoerbiger-Origa. As in the gun pump, the pump
chambers alternate such that as one is filling the other is
discharging. The shuttle timer signal 612 is also used to actuate a
4-way valve 618. Main air is reduced to a lower pressure by a
regulator 620 to produce pinch air 622 for the transfer pump pinch
valves. The pinch air 622 is delivered to the 4-way valve 618. The
pinch air is coupled to the pinch valves 624 for the one pump
chamber and 626 for the other pump chamber such that associated
pairs are open and closed together during the same cycle times as
the pump chambers. For example, when the delivery pinch valve 624a
is open to the one pump chamber, the delivery pinch valve 626a for
the other pump chamber is closed, while the suction pinch valve
624b is closed and the suction pinch valve 626b is open. The valves
reverse during the second half of each pump cycle so that the pump
chambers alternate as with the gun pump. Since the pinch valves
operate on the same timing cycle as the pump chambers, a continuous
flow of powder is achieved.
[0104] FIG. 11 illustrates an alternative embodiment of the
transfer pump pneumatic circuit. In this embodiment, the basic
operation of the pump is the same, however, now a single valve 628
is used to alternate positive and negative pressure to the pump
chambers. In this case, a pneumatic frequency generator 630 is
used. A suitable device is model 81 506 490 available from Crouzet.
The generator 630 produces a varying air signal that actuates the
chamber 4-way valve 628 and the pinch air 4-way valve 618. As such,
the alternating cycles of the pump chambers and the associated
pinch valves is accomplished.
[0105] FIG. 12 illustrates an inventive flow control aspect that is
made possible by the independent control of the pinch valves 480,
481. This illustration is for explanation purposes and does not
represent actual measured data, but a typical pump in accordance
with the present disclosure will show a similar performance. The
graph plots total flow rate in pounds per hour out of the pump
versus pump cycle time. A typical pump cycle time of 400
milliseconds means that each pump chamber is filling or discharging
during a 400 msec time window as a result of the application of
negative and positive pressure to the pressure chambers that
surround the porous members. Thus, each chamber fills and
discharges during a total time of 800 msec. Graph A shows a typical
response if the pinch valves are operated at the same time
intervals as the pump chamber. This produces the maximum powder
flow for a given cycle time. Thus, as the cycle time increases the
amount of powder flow decreases because the pump is operating
slower. Flow rate thus increases as the cycle time decreases
because the actual time it takes to fill the pump chambers is much
less than the pump cycle time. Thus there is a direct relationship
between how fast or slow the pump is running (pump cycle time based
on the time duration for applying negative and positive pressure to
the pump pressure chambers) and the powder flow rate.
[0106] Graph B is significant because it illustrates that the
powder flow rate, especially low flow rates, can be controlled and
selected by changing the pinch valve cycle time relative to the
pump cycle time. For example, by shortening the time that the
suction pinch valves stay open, less powder will enter the pump
chamber, no matter how long the pump chamber is in suction mode. In
FIG. 12, for example, graph A shows that at pump cycle time of 400
msec, a flow rate of about 39 pounds per hour is achieved, as at
point X. If the pinch valves however are closed in less than 400
msec time, the flow rated drops to point Y or about 11 pounds per
hour, even though the pump cycle time remains at 400 msec. What
this assures is a smooth consistent powder flow even at low flow
rates. Smoother powder flow is effected by higher pump cycle rates,
but as noted above this would also produce higher powder flow
rates. So to achieve low powder flow rates but with smooth powder
flow, the present invention allows control of the powder flow rate
even for faster pump cycle rates, because of the ability to
individually control operation of the suction pinch valves, and
optionally the delivery pinch valves as well. An operator can
easily change flow rate by simply entering in a desired rate. The
control system 39 is programmed so that the desired flow rate is
effected by an appropriate adjustment of the pinch valve open
times. It is contemplated that the flow rate control is accurate
enough that in effect this is an open loop flow rate control
scheme, as opposed to a closed loop system that uses a sensor to
measure actual flow rates. Empirical data can be collected for
given overall system designs to measure flow rates at different
pump cycle and pinch valve cycle times. This empirical data is then
stored as recipes for material flow rates, meaning that if a
particular flow rate is requested the control system will know what
pinch valve cycle times will achieve that rate. Control of the flow
rate, especially at low flow rates, is more accurate and produces a
better, more uniform flow by adjusting the pinch valve open or
suction times rather than slowing down the pump cycle times as
would have to be done with prior systems. Thus the invention
provides a scalable pump by which the flow rate of material from
the pump can be, if desired, controlled without changing the pump
cycle rate.
[0107] FIG. 13 further illustrates the exemplary pump control
concept of the present inventions. Graph A shows flow rate versus
pinch valve open duration (in milliseconds) at a pump cycle rate of
500 msec, and Graph B shows the data for a pump cycle rate of 800
msec. Both graphs are for dual chamber pumps as described herein.
First it will be noted that for both graphs, flow rate increases
with increasing pinch valve open times. Graph B shows however that
the flow rate reaches a maximum above a determinable pinch valve
open duration. This is because only so much powder can fill the
pump chambers regardless of how long the pinch valves are open.
Graph A would show a similar plateau if plotted out for the same
pinch valve duration times. Both graphs also illustrate that there
is a determinable minimum pinch valve open duration in order to get
any powder flow from the pump. This is because the pinch valves
must be open long enough for powder to actually be sucked into and
pushed out of the pump chambers. Note that in general the faster
pump rate of Graph A provides a higher flow rate for a given pinch
valve duration.
[0108] The data and values and graphs provided herein are intended
to be exemplary and non-limiting as they are highly dependent on
the actual pump design. The control system 39 is easily programmed
to provide variable flow rates by simply having the control system
39 adjust the valve open times for the pinch valves and the
suction/pressure times for the pump chambers. These functions are
handled by the material flow rate control 632 process.
[0109] In an alternative embodiment, the material flow rate from
the pump can be controlled by adjusting the time duration that
suction is applied to the pump pressure chamber to suck powder into
the powder pump chamber. While the overall pump cycle may be kept
constant, for example 800 msec, the amount of time that suction is
actually applied during the 400 msec fill time can be adjusted so
as to control the amount of powder that is drawn into the powder
pump chamber. The longer the vacuum is applied, the more powder is
pulled into the chamber. This allows control and adjustment of the
material flow rate separate from using control of the suction and
delivery pinch valves.
[0110] Use of the separate pinch valve controls however can augment
the material flow rate control of this alternative embodiment. For
example, as noted the suction time can be adjusted so as to control
the amount of powder sucked into the powder chamber each cycle. By
also controlling operation of the pinch valves, the timing of when
this suction occurs can also be controlled. Suction will only occur
while negative pressure is applied to the pressure chamber, but
also only while the suction pinch valve is open. Therefore, at the
time that the suction time is finished, the suction pinch valve can
be closed and the negative pressure to the pressure chamber can be
turned off. This has several benefits. One benefit is that by
removing the suction force from the pressure chamber, less
pressurized process air consumption is needed for the venturi pump
that creates the negative pressure. Another benefit is that the
suction period can be completely isolated from the delivery period
(the delivery period being that time period during which positive
pressure is applied to the pressure chamber) so that there is no
overlap between suction and delivery. This prevents backflow from
occurring between the transition time from suction to delivery of
powder in the powder pump chamber. Thus, by using independent pinch
valve control with the use of controlling the suction time, the
timing of when suction occurs can be controlled to be, for example,
in the middle of the suction portion of the pump cycle to prevent
overlap into the delivery cycle when positive pressure is applied.
As in the embodiment herein of using the pinch valves to control
material flow rate, this alternative embodiment can utilize
empirical data or other appropriate analysis to determine the
appropriate suction duration times and optional pinch valve
operation times to control for the desired flow rates. During the
discharge or delivery portion of the pump cycle, the positive
pressure can be maintained throughout the delivery time. This has
several benefits. By maintaining positive pressure the flow of
powder is smoothed out in the hose that connects the pump to a
spray gun. Because the suction pinch valves can be kept closed
during delivery time, there can be an overlap between the end of a
delivery (i.e. positive pressure) period and the start of the
subsequent suction period. With the use of two pump chambers, the
overlap assures that there is always positive pressure in the
delivery hose to the gun, thereby smoothing out flow and minimizing
pulsing. This overlap further assures smooth flow of powder while
the pinch valves can be timed so that positive pressure does not
cause back flow when the suction pinch valves are opened. Again,
all of the pinch valve and pressure chamber timing scenarios can be
selected and easily programmed into the control system 39 to effect
whatever flow characteristic and rates are desired from the pump.
Empirical data can be analyzed to optimize the timing sequences for
various recipes.
[0111] The present disclosures contemplate a dense phase pump that
is highly efficient in terms of the use of pressurized process air
needed to operate the pump. As noted above, the suction pressure
optionally can be turned off as part of the pump flow rate control
process because the pinch valves can be separately timed. This
reduces the consumption of process air for operating the venturi
pump that produces the negative suction pressure. The use of dense
phase transport allows for smaller powder flow path geometries and
less air needed to transport material from the pump to the gun.
Still further, the pinch valves operate in a normally open mode,
thus there is no need for air pressure or a control member or
device to open the pinch valves or to maintain them open.
[0112] Thus, the inventive pump design herein may be used to
provide a scalable material flow rate pump output by which is meant
that the operator can select the output flow rate of the pump
without having to make any changes to the system other than to
input the desired flow rate. This can be done through any
convenient interface device such as a keyboard or other suitable
mechanism, or the flow rates can be programmed into the control
system 39 as part of the recipes for applying material to an
object. Such recipes commonly include such things as flow rates,
voltages, air flow control, pattern shaping, trigger times and so
on.
[0113] We have discovered a number of operational and performance
characteristics of a pump that incorporates one or more of the
inventive aspects and features described hereinabove, or which may
be present in other pump designs that use porous tubes, wherein
such characteristics may result in reduced performance in some
circumstances. We have further discovered alternative and/or
optional control processes that may be used to improve these
operational and performance characteristics for not only the pump
designs described herein, but other dense phase pump designs of the
type that utilize porous barriers to alternately apply suction and
positive pressure to a pump chamber.
[0114] For example, we have discovered that because dense phase
powder is by definition a rich mixture with reduced air content,
there is a tendency for the mixture to have somewhat of an inertia
which initially resists the sucking of powder into the pump
chambers 438c, 440c in the beginning portion of a suction
condition. This inertia exists in part because the powder has been
sitting in the powder path to the pump while powder is being
delivered under pressure during the delivery portion of the pump
cycle. In accordance with an inventive aspect of this disclosure,
the suction pinch valves and related control valves may be
sequenced or timed so as to produce a suction spike of higher
energy in the beginning portion of a suction condition or time
duration. This spike helps overcome the inertia of the dense phase
powder to begin moving powder into the pump chamber. After the
initial spike the suction pressure typically will reduce to a
desired or predetermined range. The spike effect may be unnecessary
for mixtures and/or pump designs that do not exhibit the inertial
delay for powder flow into the pump chamber.
[0115] As another example, porous materials such as may be used,
for example, for the pump chamber tubes 438, 440 tend to become
obstructed over time, or "blind". This occurs simply due to the
fact that very small powder particles inevitably become lodged in
or against the porous material. Thus, over time the porosity of the
material to air flow decreases. We have discovered that the pump
tubes 438, 440 tend to become "seasoned" over a period of time and
remain somewhat in that condition for perhaps a number of hundreds
of hours of operation before becoming blinded to the point that
insufficient air flow through the porous material can be
maintained. In accordance with another inventive aspect, by early
application of a lower and optionally optimized suction force, the
time period during which the tubes "season" can be significantly
extended, thus extending the overall useful life of the tubes 438,
440. For example, the suction force applied to suck powder into the
pump chambers may be set at a level or range that is just
sufficient to ensure powder will adequately be drawn into the pump
chamber. This feature may be used optionally with the initial spike
concept described above. By using a reduced suction force the tubes
take much longer to season and thus will not blind for a longer
period of time. Note that by "early" in this context we are
referring to the useful life of the tubes and applying a suction
force applied during new pump or new tube operation, not the
initial suction time when the optional higher spike may be also
used.
[0116] In accordance with another inventive aspect, tube blinding
is compensated for by optionally implementing a flow rate control
feature. As noted above, as the tubes 438, 440 blind over time, the
flow rate of air through the porous material decreases for a given
applied force or pressure whether that pressure be suction or
delivery (delivery meaning positive pressure to push powder out of
the pump chambers.) In accordance with another inventive aspect,
flow rate control may be used to increase the applied pressure so
as to maintain a desired air flow rate, for example, to maintain a
desired or predetermined minimum flow rate to assure powder is
adequately sucked in and pushed out of the pump chamber. The
predetermined or desired values or ranges may differ for suction
and delivery or in some cases may be the same. Flow rate control
may be implemented for positive pressure delivery air flow, suction
pressure air flow, or both.
[0117] All of these inventive aspects may optionally be used
together, alone or in various combinations. Additionally they may
be used with dual pump chambers as in the exemplary embodiments
herein above, single pump chamber designs or pumps having more than
two pump chambers.
[0118] For purposes of more clearly illustrating the inventive
concepts and features noted above, we refer to various figures and
illustrations herein that exemplify the functional control aspects
for operation of a pump, such as for example, a pump as described
herein above. Even though these function and control aspects are
explained herein in the context of an exemplary pump design, those
skilled in the art will readily appreciate that these inventive
aspects may find application in many other pump designs and
configurations.
[0119] A suitable pump for explaining these enhancements is
illustrated in FIG. 14. This figure is the same embodiment as FIG.
2B hereof but with different or additional identifying numbers and
letters to highlight various control elements. The pump 402 has two
filter sleeves or porous tubes A and B which comprise the two
pumping chambers of this pump. These chambers alternately receive
powder from a powder hopper 700 and discharge that powder to a
spray gun 20. Four pinch valves control the flow of powder into and
out of these two pump chambers. There are two pinch valves for each
pump chamber. These pinch valves are marked A-in, A-out, B-in and
B-out. A-in allows powder to enter chamber A from the feed hose 24
connected to a powder hopper and A-out allows powder to be
delivered or discharged from chamber A through the supply hose 406
to the spray gun 20. Likewise, B-in allows powder to enter chamber
B from the same feed hose 24 connected to the same powder hopper
and B-out allows powder to be discharged from chamber B through the
same supply hose connected 406 to the same spray gun 20.
[0120] FIG. 15 shows an idealized timing for the delivery and
suction conditions in chambers A and B. As shown, each chamber has
a suction cycle 702 during which powder is pulled into the chamber
and a pressure or delivery cycle 704 during which powder is pushed
out of the chamber. The cycles would be about equal in duration and
chamber A and B would alternate so that while powder was being
pulled into chamber A it was being pushed out of chamber B and vice
versa. Given this mode of operation, it was deemed adequate that
the suction condition in a chamber would be a relatively constant
suction force being applied during the entire suction cycle. By
"suction condition" is meant a time period when negative pressure
exists in the pump pressure chamber.
[0121] FIG. 16 shows one of the inventive aspects wherein instead
of applying relatively constant suction force to chamber A during
the entire suction cycle, a suction condition 706 is generated in
chamber A during a portion of the suction cycle that is less than
the duration of the suction cycle. In an exemplary embodiment, the
suction condition is applied about in the middle portion of the
suction cycle, and in addition, the suction condition starts with a
spike or pulse 708 of a relatively higher suction force which then
reduces to a lower level 710 of suction force. The suction spike
overcomes the inertia of the static powder lying in the feed hose
and gets the powder moving. Thereafter, the reduced suction level
in chamber A is sufficient to keep the powder moving until the
desired amount of powder has been received in chamber A and the
suction is terminated. The same suction condition is created in
chamber B during the suction cycle for chamber B.
[0122] The concept of approximately centering the suction condition
within the suction cycle, and the concept of producing the spike,
are separate concepts that may be used together or individually as
needed for a particular application.
[0123] FIG. 17 shows an exemplary manner in which the suction
condition shown in FIG. 16 may be produced in chambers A and B. A
vacuum control valve A/B-v is activated to produce a vacuum or
negative pressure condition .sup.-P when a suction condition is
required in either chamber A or B. With respect to chamber A, a two
position valve A-s can be shifted between a positive pressure
position .sup.-P and a suction position T. During the suction cycle
702, A-s is shifted to the suction position to allow the vacuum
controlled by valve A/B-v to be applied to chamber A during a
selectable portion 706 of the suction cycle 702 that the control
valve A/B-v is generating a vacuum. To produce a suction spike such
as for example shown in FIG. 16, vacuum generator control valve
A/B-v is turned on during for example, a middle portion of the
suction cycle 702 as shown in FIG. 16, but initially pinch valves
A-in and A-out are both kept closed. This causes the vacuum
condition to build and intensify in the pump chamber A. When pinch
valve A-in is then opened to allow powder to be sucked into chamber
A from the powder feed hose 24, the powder in the hose is initially
hit with or is exposed to the suction spike 708 to overcome the
powder's inertia and get it moving. Shortly after the valve A-in is
opened, the level of the suction in chamber A drops off to a
relatively more constant lower level 710 which keeps the powder
moving into the pump chamber A. Once the desired amount of powder
is received within chamber A, the vacuum generating control valve
A/B-v is turned off and valve A-in is closed. The same suction
condition may be created in chamber B during the suction cycle for
chamber B.
[0124] The reduced suction level 710 may be controlled by way of
the valve A/B-v. This valve A/B-v may for example be a servo valve
that controls the flow of air to the venturi pump 518 or other
source of negative pressure used for the pump pressure chambers.
The amount of suction produced may optionally be a predetermined
value or range that is optimized or near optimized to a minimum
level needed to assure that powder is adequately sucked into the
powder chamber 438c, 440c during a suction condition. This minimum
or at least a reduced suction force may be determined empirically
for example, as it will be influenced by the choice of venturi
pump, valve design, powder path size and length, powder pump
chamber volume and so on. In accordance with an inventive aspect,
the reduced suction value may optionally be used to extend the
useful life of the porous tubes 438, 440 because the lower suction
force will slow down blinding of the tubes and reduce impact
fusion, as described herein above.
[0125] FIG. 18 shows exemplary timing waveforms for the electrical
signals controlling the valves for A-in, A-out, A-s and A/B-v of
FIG. 17. As shown, A-s is open to pass through any suction force
generated under control of A/B-v during the entire suction cycle.
The valve A-s shifts to this suction position at time T1 which is
the start of the suction cycle for chamber A. At time T2, A/B-v is
actuated to apply a suction condition to chamber A. At this time,
A-in and A-out are both closed so the vacuum force is allowed to
intensify in chamber A. At time T3, A-in is opened and the vacuum
force which has been building in chamber A sucks powder from the
supply hose through valve A-in into chamber A. As previously
mentioned, this suction condition optionally starts with a suction
spike which gets the powder moving and overcomes the inertia of the
powder lying in the hose. At time T4, after the desired amount of
powder has been drawn into chamber A, A-in closes to cut off the
entry of additional powder into chamber A, and at the same time
A/B-v closes to cut off the source of the vacuum. At time T5, A-s
shifts to its positive pressure position to end the suction cycle
and begin the delivery cycle, and at about the same time A-out is
opened to allow powder to be pushed out of chamber A through the
feed hose to the gun by an air pressure source indicated in FIG.
17. The delivery cycle ends at time T6 when the A-s valve shifts to
the suction position shown at time T1 to begin the next suction
cycle. Note that the suction duration (i.e. the time T2-T4) applied
to chamber A by suction source A/B-v, may be generally centered
within the suction cycle T1-T5 for reasons explained herein below.
Notice also that the suction cycle T1-T5 has about the same
duration as the delivery cycle T5-T6. This is preferred, of course,
because while chamber A is undergoing the suction cycle, chamber B
is undergoing the delivery cycle and vice versa.
[0126] With respect to FIG. 18, note that the flow rate of powder
delivered by the pump is largely determined by the duration T3-T4
which is the amount of time that valve A-in is open. The longer
A-in is open, the greater the amount of powder drawn into and
pushed out of chamber A at each cycle and the higher the flow rate
from the pump. Conversely, the shorter the duration that A-in is
open, the lower the flow rate of the pump. As noted herein above,
however, there is a practical limit to the powder flow rate after
the pinch valves are open an amount of time that fills the pump
chamber.
[0127] Notice also that the length of the suction and delivery
cycles affect the uniformity of powder flow from the pump. If the
duration of the cycles is relatively long, there is more time for a
greater amount of powder to be pulled into the pump chambers each
cycle, and when the powder is pushed out of the chambers it is more
likely to form as pulses or shots of powder with relatively long
interval between these pulses. The result of this is a pulsing
powder supply to the spray gun which is less desirable in that it
may produce a pulsing spray pattern discharged from the gun. If the
duration of the cycles is relatively short, on the other hand, then
smaller amounts of powder are pulled into the pump chambers during
the shorter cycles and these smaller volumes of powder are pushed
out of more frequently from the pump to the supply hose with
shorter intervals between these smaller pulses with the overall
effect being a more uniform flow rate of powder to the spray gun
and a better more uniform cloud of powder dispensed from the spray
gun. If the pump is run too fast, however, the frequent opening and
closing of the pinch house generates heat which can cause the
powder to cure inside the pump and can also cause premature failure
of pump components. Consequently, it is desirable to operate at a
high enough cycle rate and short enough cycle time to maintain
uniform powder flow to the gun, but at a cycle rate which is no
higher than needed to accomplish that purpose.
[0128] FIG. 19 shows further details of the pump operation and why
it is preferred to center the suction duration T2-T4 within the
suction cycle T1-T5. This figure shows typical response times for
the opening and closing of the valves in the system as shaded cross
hatched regions. The response time for closing pinch valve A-in for
example, extends for approximately 25 milliseconds after T4
(denoted as T4' on the drawing). That means once the signal is
given to valve A-in to close, the valve takes approximately 25
milliseconds to reach its fully closed condition at T4'. It may be
important in many systems that this response time be shorter than
the duration T4-T5 so that A-in is fully closed before A-s shifts
to blow powder from out of chamber A through valve A-out into the
supply hose 406. If A-in were not fully closed before this shift
occurred, some powder could be blown in the backwards direction
through A-in causing a reversal of powder flow down the supply hose
from the pump towards the hopper, which in some cases may be
undesirable. By centering the suction duration within the suction
cycle, opening and closing response times for the valves are
allowed to time out properly to avoid this type of problem. Note
that the response times for the various pinch valves A-in, A-out,
B-in and B-out may be different depending upon whether the valve is
being opened or closed or used for delivery or suction.
[0129] FIG. 19 also illustrates that the delivery valves A-out and
B-out also exhibit inherent open and close response times, however,
these pinch valves can be permitted to overlap into the subsequent
suction cycle because the suction condition is restricted to time
period T3-T4. For example, in FIG. 19, valve A-out fully closes at
time T1' which extends into the suction cycle that begins at time
T1, but since the suction condition does not occur until time T3
(really T3' allowing for response time of A-in to fully open) there
is no blow back. This allows the delivery pinch valves A-out and
B-out to overlap (compare T1' and T1'' as well as T5' and T5'') so
that optionally positive pressure is always provided to the feed
hose 406 to the gun 20.
[0130] FIG. 20 shows the optional use of a volumetric air flow rate
controller 720 to push the powder out of the chamber A. The
volumetric air flow rate controller ensures that powder is pushed
out of the chamber A at the desired rate. If the powder is pushed
out too fast, then concentrated slugs of powder form in the supply
hose to the gun and the powder is delivered in a pulsed fashion to
the spray gun which causes the gun to spray a pulsed spray pattern
which is undesirable. This is the same phenomena which can occur if
the cycle rate is too slow as described above. If the powder is
pushed out at a slower rate, the powder will be more spread out in
the supply hose to the gun which produces a more even spray pattern
at the gun. However, if the powder is pushed out the chamber too
slowly, all the powder will not be pushed out of the chamber before
the completion of the delivery cycle. Thus, the volumetric air flow
rate controller is used to push powder out of the chamber A at a
rate which is just fast enough to push all powder out of the
chamber during the delivery cycle, but no faster so that as even a
powder flow as possible is produced in the supply hose to the gun.
A volumetric air flow rate controller may be likewise installed
with respect to chamber B in the same way for a two chamber
pump.
[0131] The volumetric air flow rate controller 720 may be used to
compensate for the circumstance that over time the porous tubes
438, 440 tend to blind or become less porous to air flow. In many
situations, air flow rate through the tubes is important during
both suction and delivery cycles. It may be useful in many cases to
maintain a certain or minimum air flow rate during delivery and
suction to assure that powder is adequately sucked into and pushed
out of the tubes 438, 440.
[0132] For the delivery cycle, the positive pressure flow rate
controller 720, in an exemplary embodiment, monitors or detects a
condition related to air flow rate through the tubes and adjusts
air pressure accordingly to assure that a sufficient air flow rate
is present. With reference to FIGS. 22A and 22B, the positive
pressure flow rate controller 720 is embodied using a control servo
valve 722, a pressure transducer 724 and a fixed or control orifice
726. The pressure drop across the orifice 726 is directly related
to the flow rate of air into and through the porous tubes 438, 440.
The controller 720 monitors the pressure and if it drops below a
range that corresponds to a desired air flow rate through the
tubes, the valve 722 can be opened further to increase pressure to
the tubes to maintain adequate air flow. The control orifice 726 in
this embodiment is positioned on the high pressure or inlet side of
the valve 722 because differential pressure transducers tend to be
more accurate when one side of the orifice is a relatively stable
pressure. However, the control orifice 726 may be located elsewhere
as required. The flow rate control function may also be carried out
in many different ways other than with a valve, transducer or
orifice. It should be noted that in a similar manner, in the
embodiment of FIG. 8, the pressure transducer associated with the
pump air flow control (valve 552) may be positioned on the high
pressure side of the valve.
[0133] Blinding of the tubes also may reduce air flow rate out of
the tubes during a suction condition. In accordance with another
inventive aspect, an air flow rate controller may also be used on
the suction side of the pump operation.
[0134] It is notable that air flow rate control may optionally be
used for the positive delivery pressure cycle, the negative suction
pressure cycle, or both.
[0135] FIG. 21 shows the optional use of a volumetric air flow rate
controller 730 on the suction side of the pump in the line between
valve A-s and the A/B-v vacuum source. This controller 730 is used
in the following way. Chamber A is surrounded by a cylindrical
shaped filter element as previously described. The suction air
which pulls powder into the chamber passes through this cylindrical
filter element. Over time, the pores of this filter element can
become blinded or partially blinded by powder particles. This
blinding increases the air flow resistance of the filter element
with results that less suction force is applied to chamber A over
time if no changes are made in any other part of the system. When
less suction force applied to chamber A, less powder is pulled into
chamber A, and thus less powder is delivered by the pump to the
spray gun. The volumetric air flow rate controller is used to sense
the air flow rate of the suction air leaving chamber A to ensure
that the air flow rate remains constant, and thus, that the suction
force in chamber A remains constant regardless of any blinding or
partial blinding of the filter element. This ensures that a
consistent amount of powder is pulled into the chamber A regardless
of the condition of the filter element. This in turn helps to
maintain the powder flow rate from the pump at a consistent rate. A
similar volumetric air flow rate controller is installed with
respect to chamber B.
[0136] Again with reference to FIGS. 22A and 22B, the vacuum side
flow rate controller 730 may be realized in the form of a control
servo valve 732, a pressure transducer 734 and a control orifice
736. The pressure drop across the orifice 736 is directly relatable
to the air flow rate through the porous tubes (drawn out of the
tube volume that defines the pump chamber) during a suction
condition. In this embodiment, the controller 730 adjusts the
positive pressure that is input to the venturi pump 518 that
creates the negative pressure or suction. However, other flow rate
sensing and control techniques may alternatively be used.
[0137] The air flow rate controllers 720, 730 may operate by use of
look-up tables that relate detected pressure drops across the
control orifices with corresponding flow rates. The flow rates for
suction and delivery may be the same or different. A suitable
control function such as a programmable processor may access the
database and also produce suitable control signals such as PWM
signals to the control valves 722, 732. The valves may, on the
first operational cycle after start-up of the pump, be opened to a
default setting that produces an air flow rate across the orifices
that acts as a "seed" value. The valves are then adjusted as needed
so that the suction and delivery flow rates are kept at a desired
value or range for a particular pump operation. Another optional
control feature is that an operator interface may be conveniently
provided to allow an operator to "dial in" or adjust or select a
desired pump flow rate. This setting results in the control system
39 adjusting the air flow rates needed to achieve the desired pump
operation.
[0138] FIGS. 22A and 22B show that the servo valve 732 is used to
modulate the air source feeding the vacuum generator 518 and not
directly modulating the vacuum output. This may be done for at
least two reasons: a) there is a relatively wide linear
relationship between input pressure and the resulting vacuum
output; and b) the servo has much more source pressure (for
example, up to about 85 psi) to modulate than if it were
controlling the vacuum pressure directly (i.e. a source pressure of
about -8 psi for example). The differential pressure transducer
selected is also different from the ones used in the other air flow
control circuits because of this relatively small vacuum pressure
level. The selected differential transducer's range of operation is
from 0 to 0.57 psi. In this case, only about 7% of the available
vacuum is lost as a drop across the sensor, for example.
[0139] Given the features and capabilities of the pump described
above which work together to ensure that a uniform flow rate of
powder can be provided by this pump over a wide range of powder
flow outputs, yet another novel aspect of this pump is its
capability of providing recipes which can be used to tailor the
powder flow from the pump in an optimal way for the particular
application for which the pump is being used. The pump powder flow
recipes can contain the following parameters: suction cycle
duration (T1-T5), suction duration (T2-T4) and flow rate setting
for air used to push powder out of the chambers. Numerous powder
flow recipes 800 (FIG. 1) for various applications can be stored in
a suitable data structure 802 as a look up table for quick access
as needed by the user.
[0140] The inventions have been described with reference to the
exemplary embodiments. Modifications and alterations will occur to
others upon a reading and understanding of this specification and
drawings. The inventions are intended to include all such
modifications and alterations insofar as they come within the scope
of the appended claims or the equivalents thereof
* * * * *