U.S. patent application number 11/999893 was filed with the patent office on 2008-06-26 for reciprocating antirotation pump.
Invention is credited to Jeffrey A. Karg, Vanessa Kollars, Paul Simonetti.
Application Number | 20080152515 11/999893 |
Document ID | / |
Family ID | 39543061 |
Filed Date | 2008-06-26 |
United States Patent
Application |
20080152515 |
Kind Code |
A1 |
Karg; Jeffrey A. ; et
al. |
June 26, 2008 |
Reciprocating antirotation pump
Abstract
A pump for pumping discrete liquid volumes is provided with an
anti-rotation construction to prevent a nut mated to a rotating
head screw from rotating when the lead screw is rotated. The
anti-rotation construction comprises a set of rails that slideably
fit within a mating set of tracks. The pump also can include a
variable homing position for a pump piston having at least two
different homing positions.
Inventors: |
Karg; Jeffrey A.;
(Hopkington, MA) ; Simonetti; Paul; (Cotuit,
MA) ; Kollars; Vanessa; (New Bedford, MA) |
Correspondence
Address: |
Paul J. Cook
115 Pine Street
Manchester
MA
01944
US
|
Family ID: |
39543061 |
Appl. No.: |
11/999893 |
Filed: |
December 10, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60876413 |
Dec 21, 2006 |
|
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|
Current U.S.
Class: |
417/415 ;
417/321; 417/437 |
Current CPC
Class: |
F04B 35/045
20130101 |
Class at
Publication: |
417/415 ;
417/321; 417/437 |
International
Class: |
F04B 35/04 20060101
F04B035/04 |
Claims
1. A pump adapted to deliver a plurality of discrete liquid samples
comprising a motor adapted to rotate a shaft including a lead screw
clockwise or counter clockwise, a nut mated to said lead screw
adapted to reciprocate when said lead screw is rotated, a first
housing for said nut having an outside surface provided with either
a first set of rails or a first set of tracks, a second set of
tracks positioned on a stationary housing positioned to mate with
said first set of rails or a second set of rails positioned on said
stationary housing to mate with said first set of tracks, a pump
piston mounted on said first housing, said first set of tracks or
said second set of tracks having a length sufficient to permit said
piston to travel a desired distance when said motor is rotated.
2. The pump of claim 1 wherein said first housing includes said
first set of rails.
3. The pump of claim 1 wherein said first housing includes said
first set of tracks.
4. The pump of claim 3 wherein said second set of tracks are
positioned on removable inserts that are attachable to said
stationary housing.
5. The pump of claim 2 wherein said second set of tracks is
positioned on an inner surface of said stationary housing.
6. A pump adapted to deliver a plurality of discrete liquid samples
and having a variable homing position for accepting a visible
homing flag in one of at least two positions.
7. The pump of claim 6 having two of said positions for said homing
flag.
8. The pump in claim 2 having an anti-backlash nut feature
integrated into the ferrule.
9. The pump in claim 2 having two heads actuated by a dual shaft
motor with shafts protruding from both sides of the motor.
Description
REFERENCE TO RELATED APPLICATION
[0001] This application is based on provisional application Ser.
No. 60/876,413, filed Dec. 21, 2006.
BACKGROUND OF THE INVENTION
[0002] This invention relates to a reciprocating pump capable of
dispensing discrete microliter or milliliter liquid reagents. More
particularly, this invention relates to such a pump which converts
rotational motion to linear motion while utilizing an
antirotational device.
[0003] The science and economics of invitro diagnostic (IVD)
testing has changed with developments in assay reagent variation
and assay size miniaturization. The number of assays performed
annually is increasing as population demographics change and the
availability of diagnostic testing increases throughout the world.
Instrumentation is constantly adapted to these changing conditions.
The reagents are harsher, including increased usage of salt
solutions and acid and alkaline solutions having significant pH
ranges. The liquid that pumps must move is decreasing from
milliliters in volume to microliters in volume while precision and
accuracy requirements remain constant. Lastly, the instrumentation
is required to perform more tests prior to regular or unscheduled
maintenance.
[0004] Pumps are used to move fluids within IVD instrumentation and
to transfer reagents from a source reservoir to one or more test
sites. As the assay volume decreases, more precise pumps are
required. However, more precise pumps are more expensive to
manufacture. Presently, there is an acute need for a precise and
accurate pump that is also economical.
[0005] Piston pumps have been used in fluid dispensing applications
for many years and four principle areas have consistently
contributed to manufactured cost. They are the motor, the piston,
the seal, and the anti-rotation mechanism. In addition, presently
available pumps having a home position for the pump piston to
provide a base value for the computer processing unit (CPU) which
controls piston movement. Pumps are available with the piston home
position being either in the piston aspirated position or in the
piston retracted position. Accordingly, it would be desirable to
simplify the anti-rotation mechanism by designing each part to be
multi-functional and manufacturable with multiple processes
including machined and injection molded methods. The manufacturing
process flexibility helps to control costs during the initial time
period prior to high volume production. In addition, it would be
desirable to provide the pump user with a choice for the piston
home position to provide flexibility in choosing a desired CPU.
SUMMARY OF THE INVENTION
[0006] The present invention provides a pump for liquids which
utilizes a rotary motor capable of rotating clockwise and
counterclockwise, a reciprocation pump piston and means for
converting rotary motion to reciprocating linear motion. A lead
screw which mates within a nut portion of a ferrule is rotated by
the motor. The nut portion of the ferrule moves linearly and drives
a piston portion of the pump to deliver discrete volumes of liquid.
An antirotational construction is provided which prevents rotation
of the nut portion of the ferrule. The dispense resolution of a
pump, commonly stated as microliters per step, is proportional to
the pitch of the lead screw. Since most piston pumps are built with
off the shelf linear actuators, lead screw pitch is limited to
those offered by the linear actuator manufacturer. This invention
incorporates a standard stepper motor with a custom machined lead
screw that is pressed onto the shaft enabling an infinite range of
dispense resolutions.
[0007] The antirotation construction comprises a set of rails that
fit into tracks. Either the rails or tracks can be positioned on
the nut portion of the ferrule and the mating rails or tracks are
positioned on a stationary housing for the nut portion of the
ferrule. The length of the rails and tracks permits the pump piston
to reciprocate between a fully aspirated position and a fully
retracted position.
[0008] Variations in pump construction allow for additional
features. The nut in the ferrule can be slotted and combined with a
single or multiple o-rings as springs to provide low-cost
mechanical anti-backlash compensation. In addition, the stepper
motor which turns the lead screw can be made with a shaft
protruding on both sides to provide two pump heads that are
controlled simultaneously with one motor.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is an exterior isometric view of the pump of this
invention.
[0010] FIG. 2 is an exploded isometric view of the components of
the pump of FIG. 1.
[0011] FIG. 3 is a side cross sectional view of the pump of this
invention.
[0012] FIG. 4 is a cross section view through the rail and track of
the ferrule of this invention.
[0013] FIG. 5 is an isometric view of the anti-backlash nut
mechanism.
[0014] FIG. 6 is an isometric view of a two headed pump on one
stepper motor.
DESCRIPTION OF SPECIFIC EMBODIMENTS
[0015] In accordance with this invention, a piston reciprocating
pump is provided with a variable homing switch location. The homing
switch location can be either the fully aspirated position of the
reciprocal piston or the fully retracted position of the reciprocal
piston.
[0016] Referring to FIGS. 1 and 2, the pump 10 of this invention
comprises a rotary motor 12 adapted to rotate clockwise or
counterclockwise. The piston 3 begins to reciprocate when the motor
12 turns the lead screw 16 within the nut portion 18 of the ferrule
20. The ferrule 20 is kept from rotating by the rails 32 and 33
which fit into tracks 28 and 30, which, in turn, causes the piston
22 to move back and forth.
[0017] The shaft 14 is attached to lead screw 16 so that when the
shaft 14 is rotated, the lead screw 16 is rotated. Lead screw 16
mates with threaded nut portion 18 positioned within the ferrule
20. Piston 22 is secured to the ferrule 20 so that when the nut
portion 18 moves linearly during rotation of screw 16, piston 22
also moves linearly. A wash disk seal 24 fits into pump head 26 and
provides the sealing function to permit liquid to be pumped in
discrete volumes.
[0018] The costly components within a pump 10 are the motor 12, the
piston 22, the seal 24, and the anti-rotation mechanism described
herein. This invention focuses on simplifying the anti-rotation
mechanism and homing switch location by designing each part to be
multi-functional and manufacturable with either machined or molded
process.
[0019] The antirotation mechanism which prevents rotation of the
ferrule 20 comprises tracks 28 and 30 on ferrule 20 which mate with
rails 32 and 33 on inserts 34 and 35 which extend through openings
36 on fixed housing 38. The inserts 34 and 35 are fixed to housing
38 such as with screws. It is to be understood that the tracks 28
and 30 also can be located on inserts 34 and 35 while the rails can
be located on ferrule 20 to achieve the same antirotational effect.
The housing 38 is provided with two incubation posts 40 and 42
which mate with an indicator 44 or 46 which identifies the home
position of the piston for a given CPU.
[0020] The ferrule 20 which connects the piston 22 to the lead
screw 16 enabling the piston 22 to reciprocate, is now a single
piece. The housing 38 also contains the tracks 28 and 30 that fit
into a rail 32 or 33 on inserts 34 and 35 to prevent rotation of
ferrule 20. The nut half of the lead screw 16 nut drive mechanism
is also a feature on the ferrule, making the ferrule
multi-functional on three levels. The ferrule 20 holds the piston
32, incorporates the tracks 28 and 30 for anti-rotation, and
incorporates the nut 18 for reciprocation. This eliminates parts,
simplifies construction, allows for machined or molded
construction, and lowers manufacturing costs.
[0021] The housing 38 which is the most costly component to
manufacture by the machining process, is also designed for
injection molding. The housing 38 connects the motor 12 to the pump
head 26 and incorporates the ferrule 20 and homing switch 48. The
ferrule 20 which is universal for all pistons, mates to rails 32
and 33 in the universal body 38 to prevent rotation of the nut 18.
The homing switch 48 mounts in a cavity on the side of the housing
38. The multi-functional housing design simplifies construction,
allows for machined or molded construction and lowers manufacturing
costs.
[0022] Long life is a desirable trait for a piston pump. An
important component to long life is material selection. The ferrule
20 slides onto the rails 32 and 33 and the lead screw 16 rotates
within the ferrule 20. These friction points can wear and
contribute to short pump life.
[0023] In one embodiment of the invention, the rails 32 and 33 are
made of Delrin AF available from DuPont, which is generically
acetal with a polytetrafluoroethylene (PTFE) additive and the
ferrule 20 is made from polyetheretherketone (PEEK). These surfaces
exhibit good wear characteristics and persons skilled in the art
would recognize that many combinations of materials would also
perform satisfactorily. Grease is commonly applied to these
surfaces.
[0024] The pitch of the lead screw 16 is typically either 20 or 40
threads per inch and persons skilled in the art would also
recognize that a variety of pitches ranging from 2 through 100
threads per inch are possible.
[0025] In addition, persons skilled in the art would recognize that
all the parts in the pump could be manufactured with a variety of
processes including, but not limited to, machinery, plastic or
metal injection molding, rolling, stamping, or extruding.
[0026] Referring to FIG. 3, the pump 10 which includes the lead
screw 16 and the nut portion 18 of the ferrule 20 also includes two
switch homing positions 40 and 42 also includes indicator posts 41
and 42 on home indicator 48.
[0027] Referring to FIG. 4, rails 32 and 33 fit into tracks 28 and
30 of ferrule 20.
[0028] Referring to FIG. 5, the nut 18 portion of the ferrule 20 is
machined with four slots, creating four fingers 19 that can flex
inward toward the lead screw 16. When combined with one or more
o-rings 21 that compress the fingers 19 into the lead screw 16,
backlash is eliminated between the lead screw 16 and the nut 18.
Persons skilled in the art would also recognize other anti-backlash
methods may be incorporated into the ferrule 20 to eliminate
backlash and that other spring methods may be employed. In
addition, the ferrule 20 may be manufactured by machining, molding,
or other methods and may incorporate between two and twelve fingers
19.
[0029] Referring to FIG. 6, the motor 12 may be built with shafts
14 protruding from both sides of the motor 12. Some pump
applications require two liquids to be pumped in different volumes
at the same time. This allows one motor 12 to drive two pump heads
26 for that application. Persons skilled in the art would also
recognize the lead screw 16 on either side of the motor 12 could be
different, creating different dispense and aspirate profile curves.
For example, one lead screw 16 could be a left hand thread while
the other could be right hand thread. This would make both pump
heads 26 dispense and aspirate simultaneously. In another example,
both lead screws could be right hand thread. This would make one
pump head 26 aspirate while the other dispenses and vice versa when
the motor 12 direction is reversed.
* * * * *