Note: Descriptions are shown in the official language in which they were submitted.
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APPARATUS FOR METERING AGRICULTURAL CHEMICALS
FIELD OF THE INVENTION
The invention relates to a method and apparatus for providing controlled rate
distribution
of liquids or liquid suspensions of fine solids for such agricultural
purposes. Such
purposes include fertilization and growth regulation of crops and eradication
ofunwanted
plant life in a crop field.
BACKGROUND OF THE INVENTION
Wet blade agricultural liquid distribution systems rely on the rapid uptake of
liquids that
occurs in freshly cut plants at the wounds. An order of magnitude reduction in
the
concentration of agricultural liquids is possible by applying the liquids
essentially
simultaneouslywith cutting. To accomplish this, liquid dispersal mechanisms
have been
incorporated into mowers. The advantages of this system are described in
pending patent
application PCT/US96/13362, published as WO 97/06664.
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Peristaltic pumps are pumps of choice when flow rates are moderate and either
corrosive, toxic or sterile liquids are pumped. The peristaltic pump utilizes
the fact that the
liquid to be pumped resides in a flexible tube. A length of tube is placed
inside a rigid semi-
cylinder. See Figure 1. A rotating hub at the center of the cylinder drives a
roller against the
tube causing a flexure in the tube to travel in the direction in which the
impeller hub rotates.
For clarity, an impeller with a single roller is illustrated. As the flexure
of the tube is relieved
after the compression of the passing roller, a partial vacuum forms, drawing
liquid from the
intake side. The flow rate of liquid through the tube depends on the size and
elastic
properties of the tube, the hub rotation speed, the number of rollers, the
viscosity of the fluid
being pumped and the amount of tube compression. Tube compression depends on
the size
of the roller and the impeller arm dimension relative to the center of the
cylinder.
This pumping system is preferable for use with vegetation control liquids
because it
can handle a variety of liquids and because human contact with some liquids is
undesirable
for safety reasons. If a conventional pumping system were used for both
herbicides and
fertilizers, extensive flushing of the system would be required between
application of the two
materials. With a peristaltic pump, the tubing associated with each chemical
can be changed.
The pump mechanism never directly contacts the pumped material. The part most
subject
to wear is the tubing, which is inexpensive to replace when necessary.
Field experience with this system resulted in the identification of several
problems.
Normally, peristaltic pumps run at a constant rate. In this agricultural
application, the rate
must change as the mower slows to turn or in response to variable terrain. A
first solution
of this problem was to replace the motor driving the peristaltic pump with a
stepper motor.
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Step pulses drive the motor in harmony with the motion of the mower. With this
improvement, wet blade distribution was practical. With varying materials,
large changes in
flow rates are often needed. To achieve integer multiples of a base flow rate
for a given tube
size, a plurality of tubes may be stacked in the cylinder. A tube coming from
the source tank
can be split into a manifold. The stack of tubes may be introduced into the
cylinder. The
number of tubes in the stack are limited by the height of the cylinder and
roller. The output
side of each tube can be distributed to appropriate nozzles or recombined with
a manifold for
material application.
Different size tubes can be used to achieve flow rates intermediate to the
multiple
tube manifold approach. A larger tube and compatible smaller diameter roller
can be used
to adjust flow rates.
Currently available peristaltic pumps are not designed for the field
conditions
encountered in the wet-blade distribution of agricultural chemicals. Even with
the stepping
motor regulator, there are problems in maintenance, set up and fine flow
regulation. To make
modifications in the field, the peristaltic pump is disassembled. The
disassembly/reassembly
process is problematic even for simple periodic maintenance like pump
lubrication. Access
to the pump mechanism requires removal of multiple machine-screws. Reassembly
requires
thumb screw adjustment of ferrules through which the tube is threaded. Too
much pressure
on the thumb screw causes the tube to constrict changing pump characteristics;
too little
pressure causes loss of control of the loop size within the pump. In addition,
the screw mars
the tube surface and if over tight, cuts the surface unacceptably. Disassembly
to change tube
size requires removing many small machine-screws.
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OBJECTS OF THE INVENTION
The principal object of this invention is to provide an apparatus for metering
agricultural chemicals in a wet blade distribution system that can be easily
set up in the field
to handle a wide variety of distribution rates and fluid viscosities.
Another object of this invention is to provide an apparatus that can react to
various
mower speed over the terrain.
Another object of this invention is to provide a modular peristaltic pump unit
that is
readily interchangeable.
A further object of this invention is to provide a peristaltic pump apparatus
that is
easy to maintain in the field.
Another object of this invention is to provide an improved method for metering
agricultural chemicals in a wet blade distribution system.
SUMMARY OF THE INVENTION
The invention consists of a modular peristaltic pumping system that uses an
associated microprocessor-based servomechanism for controlling fluid chemical
distribution.
The microprocessor stores: the number of modules attached, the roller axis
setting, the
elastomeric properties of the tubes used, the fluid properties of the material
being pumped
and the desired distribution rate for the agricultural objective. Real time
inputs to the
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processor include the ground speed of the mower and the angular velocity of
the impellers.
From this data, the required impeller speed can be continuously calculated.
This data and the
characteristics of a DC motor are continuously used to calculate a data stream
representing
the needed motor speed. A digital-to-analog converter with appropriate
buffering then drives
the motor. The motor shaft drives the impellers in each pump module. The
peristaltic
modules are mounted on a frame. The motor is mounted to the frame. The motor
shaft ends
in a bit, similar to a screwdriver bit, that engages a mating slot in the
first module. The shaft
of the module engages the module's impeller and exits the module in a bit that
is appropriate
to engage a mating slot in the next module. Thus, modules can be ganged to
permit an
integer number of base distribution rates. Modules can be assembled on the
frame without
tools. Modules may be lubricated without tools. Modules can be disassembled
without tools
to change the tube or modify the effective impeller arm length.
Alternatively, a transmission may be provided between the motor shaft and the
drive
shaft of the peristaltic pump stack. The transmission may consist of a gear
train or one or
more pulleys and belts. In this case, the drive shaft of the transmission ends
in a bit that
engages a mating slot in the first module.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention may be better understood by reference to the following
detailed
description and to the accompanying drawings in which:
Figure 1 is a schematic cross-section of a prior art peristaltic pump for
reference
purposes.
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Figure 2 is a side view face of the module without the shaft in place.
Figure 3 is a side view of the impeller removed from the module.
Figure 4A is a side view of the impeller.
Figure 4B is a cross-section of the impeller.
Figure 5 is an end view of the shaft at the bit end.
Figure 6 is a side view of the shaft, with the orientation of Figure 5.
Figure 7 is an end view of the shaft at the slot end.
Figure 8 is a side view of the shaft, rotated 90° from Figures 5, 6,
and 7.
Figure 9 is similar to Figure 2 with the location of cross sections BB and CC
added.
Figure 10 is a cross-section of the module taken along line B-B of Figure 9.
Figure 11 is a cross-section of the module taken along line C-C of Figure 9.
Figure 12 is an enlarged cross-section of the ferrule shown in Figure 10.
Figure 13 is an end view of the ferrule.
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Figure 14 is a top view of the module.
Figure 15 is a side view of the module of the slot face showing without the
shaft in
place.
Figure 16 is a bottom view of the module.
Figure 17 is a top view of an assembly of three modules mounted on a frame
with the
motor in place.
Figure 18 is a side view of the slot face of the module resting on and
attached to a
frame.
Figure 19 is a schematic diagram of a computer-based servomechanism for
controlling the pumping rate of the invented modules.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The present invention now will be described more fully hereinafter with
reference to
the accompanying drawings, in which a preferred embodiment of the invention is
shown.
This invention may, however, be embodied in many different forms and should
not be
construed as limited to the embodiment set forth herein; rather, this
embodiment is provided
so that this disclosure will be, thorough and complete, and will convey the
scope of the
invention fully to those skilled in the art. Like numbers refer to like
elements throughout.
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Figure 1 shows the basic elements of a peristaltic pump 10 as found in prior
art. An
elastomeric tube 12 is mounted against a rigid cylinder 14. The axis of the
cylinder has a
rotating hubl6 driving a radial arm 18. A roller 20 at the end of the arm has
the appropriate
dimension to compress the tube as the arm rotates. When the tube regains its
shape after the
passage of the roller, a pressure reduction occurs on the intake side 22. This
pressure
reduction results in the pumping action.
Figure 2 shows the slot face of the module 24 housing the improved peristaltic
pump
of the invention. The housing consists of two pieces: the proximate housing
part 26 and the
distal housing part 28 that fit together like a clam shell. The proximate
housing is shaped for
mating to a frame, not shown and contains mounting bore 30. In the two outside
corners of
the proximate housing and the two outside corners of the distal housing,
standoffs 32 are
positioned to increase the stability of a multiple module stack when mounted.
On the left side
of the module is a keeper 34. The keeper consists of a keeper mount 34a
attached to the
proximate housing, a receiver bracket 34b attached to the distal housing, and
an elastic hasp
34c. The two housing parts are separated by grasping the hasp and stretching
it until a tee-
shaped thick portion of the hasp can clear the receiver bracket 34c. Once the
left edges of
the two housings are freed, they separate easily since the right edges are
joined by any
convenient tool-less means, for example, angled tongue and groove. Ferrules 64
slide over
the tube 12 and into holes in the distal housing. The rigid cylinder 14 is
indicated by hidden
line 36. The tube is in contact with the proximate housing along this line.
The impeller 38
is shown hidden by lines partly inside both housing parts and proj ected to
the right. Bushing
40 surrounds the hole that receives the shaft.
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The function provided by the elastic hasp is to give the operator the ability
to
disassemble a pump assembly in the field without tools and without handling
small parts.
Figure 3 shows the impeller 38 that serves the purpose of the radial arm 18 in
Figure
1. The bore 42 in the impeller is hexagonal to ensure positive coupling from
the bit that
drives the shaft slot. There are six small holes, 44 in the impeller face to
receive pins that
mount the two rollers. Rollers are mounted in 44a, 44a'; 44b, 44b' or 44c,
44c'. Mounting
in 44a, 44a' provides the greatest tube compression. There is about a 30%
change in
effective length of the radial arm from position 44a, 44a' to 44c, 44c'
illustrated here.
Figure 4 shows a cross section AA of the impeller. Pins 46 (right side pin
shown)
mount, for example, in position 44b, 44b' (as shown) hold rollers 48 (left
side roller shown).
Alternatively, the pin and roller may be combined in a roller subassembly
wherein the pin is
spring-loaded and retracts into the assembly when the roller position is being
changed instead
of the separate parts illustrated here.
The function provided by an impeller pin positions 44 is the ability to
flexibly set the
1 S pumping rate within a module. With the illustrated roller arrangement, the
tube compression
can be varied from about 36% to about 50% of the tube diameter.
Figures 5, 6, 7, and 8 illustrate the shaft 50 in four views. Figure 5 is a
view of the
bit end of the shaft. The bit will engage the slot of the next module, if any,
when multiple
pumps are mounted on a frame. Figures 5, 6 and 8 show the bit 78 in three
views. Figures
6 and 8 show the bearing surface 52 whose diameter approximately corresponds
to the
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inscribed circle of the hexagonal cross section portion 54 of the impeller
shaft 50. Circular
bearing surface 56 has a diameter that approximately corresponds to the circle
through the
vertices of the hexagon. The shaft expands to a shoulder region 58 that
contains slot 60.
Figure 7 is view of the slot end of the shaft, showing slot 60. Figure 8 shows
the shaft,
rotated 90° from the view in Figure 6.
The function provided is the ability to flexibly set base pumping rates by
attaching a
variable number of modules. The bit and slot uniquely enable the mower
operator to remove
and insert the modules on the module frame without tools. The shaft drives all
modules at
the same rotational speed. Other methods of ganging the modules do not offer
the ability to
remove a module from the middle of an assembly of modules. For example, a
hexagonal-
shaped bit and corresponding cavity would allow only the end module to be
removed from
the set.
Figure 9 again shows the slot face of the pump module 24 but with the
locations of
section BB and CC indicated. In addition, lubrication aperture cover 62 is
numbered.
Lubrication appropriate to the tube and roller materials may be sprayed with
an
aerosol sprayer or pumped with an oiler into the lubrication aperture 68
without removing
the module from the frame.
Figure 10 and 11 show cross sections of the module. Figure 10 is the cross
section
through the tube 12 and ferrule 64. Note the section through the proximate
housing 26
intersects a portion of the rigid cylinder. Figure 11 is the cross section
through the centerline
CA 02384371 2004-12-23
of the module. 'Ibis cross section shows the bushings 40 and 66 in a fine
crosshatch. Note
that the bore in bushing 40 is larger than the hare in bushing 66. Bushing 40
is the slot..side
bushing and the shoulder of the shaft 58 rides an this bushing- The bore
diameter is
approximately the same as the circle fhat insects the vertices of the shaft's
hexagonal cross
section. The bore in bushing 66 is approximately the same as the ineludad
circle of the
shaft's hexagonal cross section. Figure 11 also illustrates the lubrication
apezture 80 and the
cmss section of the lubrication aperture cover 62.
Figure 12 and 13 present two views of ferrule 64_ The ferrule has a section
which is
pliant. The female slides aver the elastomeric tube with the smaller diameter,
a pliant portion
toward the pump module. The femrle ,fides into the corresponding born in the
housing. Tn
doing so, pliant forgers in the female press against the tube, securing it in
place. Figure 13
illustrate that wail of the distal diameter pot'tion of the'ferrule have
notches every 60° along
the circumference. These notches allow the ferrule to collapse around the tube
somewhat,
holding it firmly in place without machine-screws.
The function provided is the ability to chance tubes in the f eld without
tools. The
length of the tube that rests against the rigid cylinder in the module can be
easily Fxed so that
it stays in place during distribution of materials.
Figure 14 shaves the housing of the improved pump from the top. The tube and
ferrules have been omitted in order to more clearly present the hasp
arrangement that permits
2D the housing to be serviced in the fteld withouttools_ The elastic hasp 34c
engages the keeper
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34b where it widens. The hasp pivots in keeper mount 34a. The hasp 34c is
operated by
grasping the handle, the tee-shaped portion at the bottom and stretching the
it until the wide
portion clears the keeper 34b. Figure 15 is a view of the outside of the slot
side of the pump
module given to reference Figures 14 and 16. Figure 16 is a view of the bottom
of the
module with a preferred method of minimizing mechanical movement of mounted
modules,
stand off 32 illustrated. In this embodiment, stand off 32 is a standard
machine-screw. The
space magnitude is determined by the length of the standard screw and the
depth of the
threaded cavity in the module housing.
Figure 17 shows the angle rail 68 and channel 70 that form the critical
elements of
the mounting frame 72. Structural angle 68 has holes drilled on appropriate
centers for
aligning with the pumping modules. The rail 68, channel 70 and DC motor 27 are
mounted
to frame components that are not shown. The DC motor has a shaft encoder, not
shown.
Three modules are shown in position on rail 68. The mounting bores 30 are
positioned over
the corresponding hole in the rail 68. The rightmost module also illustrates
the mounting
snap assembly 76. The snap assembly consists of a pin with the diameter
consistent with
mounting bore 30. The head of the pin 76a has a larger diameter so that it
will seat on the
pump module. A U-shaped snap can pivot in the head of the pin. The delta-
shaped
connection gives way to the U-shape in the orthogonal view.
The function provided by a pin-snap mechanism76 for precise alignment of
modules
is the ability for the operator to accurately position a module on a simple
frame in
juxtaposition to leading and trailing modules in such a way that drive
coupling is assured.
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Figure 18 shows the slot face of the module with the module resting on the
angle 68
and the channel 70. The U-shaped portion of the snap is easily seen in this
view.
Figure 19 is a diagram of the servomechanism. Software running on the CPU 78
calculates the appropriate voltage to drive the DC motor 74, based on ground
speed, loaded
S details concerning the agricultural objective and the actual shaft velocity
of the motor. The
response times and gain of this loop are engineered, by conventional means, to
assure
stability so the motor speed will not hunt, continuously change without the
change of any
input.
The continuous servomechanism control, Figure 19, is superior to the
unimproved
stepper motor control because the pumping action results from the elastic
recovery of the
tube just released from roller pressure. The unimproved stepper might advance
the impeller
1 ° every minute. During the minute, the impeller is stationary. In the
improved system, the
motor can run at 1 ° per minute. The elastic recovery is monotonic
(although not linear at
very low speeds) and continuous. In the unimproved stepper realization, the
distribution rate
becomes granular, available only at discrete rates particularly at slow rates.
In these systems
slow rates are extremely important as the mower slows to reverse direction or
to
accommodate terrain conditions.
Since the servomechanism is microcomputer-based, parameters that vary only at
set-
up time can be easily input and retained for the duration of the setup.
Parameters can be
input by the mower operator by keypad and/or captured in other well-known
ways. For
example, the viscosity-temperature profile of a number of materials can be
retained in the
system. The operator would need only to key in the identification number of
the materials.
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Alternatively, the number can be entered by scanning a bar code on the
material container
with a wand attached to the computer.
Field set up of integer-multiples of base distribution rates are achieved by
the modular
pumping package, Figure 17 and 18.
In a specific agricultural operation, the fluid to be dispensed and a desired
distribution
rate is specified be the agricultural objective (a growth rate, fertilization
need, herbicidal need
etc.). Referring to Figure 17, field set up proceeds as follows:
Referring also to Figure 9, after removing the module from the frame 72 by
removing
the pin-snap 76, the housing parts 26 and 28 are separated by grasping the
elastic
hasp 34c and stretching it until it clears the receiver 34b. The two pieces
easily
separate.
2. The existing pumping tube 12 is removed by sliding the shaft 50 out of the
impeller
module 24 and removing the impeller. The ferrules 64 are slid off the tube and
retained, if desired. The old tube is removed.
3. Also referring to Figure 4, based on the agricultural requirement, the
rollers are reset
if necessary by removing the roller retainer pins 46, repositioning the
rollers and
replacing the pins in the impeller.
4. The new tube is fed through the holes in the smaller housing and the
ferrules are slid
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over the appropriate ends of the tube. The impeller is placed in the loop of
the tube
and secured into module 24 by inserting the shaft, bit end first through the
larger
bushing first. Note: It will not go in any other way.
5. The housing parts are joined with the elastic hasp 34c.
6. The ferrules 64 are adjusted to assure that the tube loop 12 rests without
binding in
the cylindrical section of the proximate housing 9.
7. The reassembled module is placed on the rails of the frame 72. Rotating the
shaft
may be necessary so that the bit and slot align with the other modules already
in
place.
8. The pin-snap 76 is then inserted into the mating hole in the frame. This
insures
appropriate spacing. The snap is closed.
SUMMARY OF THE ACHIEVEMENT OF THE OBJECTS OF THE
INVENTION
From the foregoing, it is readily apparent that I have invented a method and
an
apparatus for metering agricultural chemicals in a wet blade distribution
system that can be
easily set up in the field to handle a wide variety of distribution rates,
fluid viscosities, and
mower speed over the terrain, moreover, the method and apparatus provides a
modular
peristaltic pump unit that is readily interchangeable and easy to maintain in
the field.
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In the drawings and specification, there have been disclosed typical preferred
embodiments of the invention and, although specific terms are employed, they
are used in a
generic and descriptive sense only and not for purpose of limitation, the
scope of the
invention being set forth in the following claims.
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