U.S. patent number 3,760,639 [Application Number 05/299,552] was granted by the patent office on 1973-09-25 for pipette assembly.
This patent grant is currently assigned to Bio/Data Corporation. Invention is credited to Frederick M. Kent, Michael Sokol.
United States Patent |
3,760,639 |
Sokol , et al. |
September 25, 1973 |
PIPETTE ASSEMBLY
Abstract
A pipette assembly for accurate aspiration and discharge of
fixed amounts from a pipette tip is disclosed. A spring-biased
cylinder is mounted for rotation about its longitudinal axis for
selecting the desired volume of liquid to be discharged. A variable
volume control chamber is defined between the ID of the cylinder
and the OD of a stationary piston rod. Reciprocation of the
cylinder varies the volume of the control chamber.
Inventors: |
Sokol; Michael (Abington,
PA), Kent; Frederick M. (Warrington, PA) |
Assignee: |
Bio/Data Corporation (Hatboro,
PA)
|
Family
ID: |
23155295 |
Appl.
No.: |
05/299,552 |
Filed: |
October 20, 1972 |
Current U.S.
Class: |
73/864.18;
422/927 |
Current CPC
Class: |
B01L
3/0231 (20130101) |
Current International
Class: |
B01L
3/02 (20060101); B01l 003/02 () |
Field of
Search: |
;73/425.4R,425.4P,425.6
;222/43,309,386 ;128/218A,218R,218C,218F,234,236 ;23/259,292 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Swisher; S. Clement
Claims
We claim:
1. A pipette assembly comprising a housing having first and second
ends, a pipette tip support coupled to said first end of said
housing, said support having a bore therethrough, a stationary
hollow rod in said housing and communicating with said bore, a
cylinder in said housing surrounding said rod and spaced therefrom
to define a chamber of variable volume, the volume of said chamber
increasing when said cylinder moves toward said pipette tip
support, sealing means between said rod and cylinder for sealing
the ends of said chamber, spring means biasing said cylinder away
from said pipette tip support to effect a decrease in the volume of
said chamber, said rod having a passage communicating with said
chamber, and limit stop means for limiting the extent of movement
of said cylinder in a direction away from said pipette tip support
due to the bias of said spring means.
2. A pipette assembly in accordance with claim 1 wherein said limit
stop means is selectively operable to limit the extent of movement
of the cylinder in a direction away from the pipette support to
predetermined distances.
3. A pipette assembly in accordance with claim 2 wherein said limit
stop means includes an adapter supported by said housing, said
adapter having a plurality of recesses of different depths, each
adapted to receive the limit stop member on said cylinder.
4. A pipette assembly in accordance with claim 1 wherein said
cylinder is rotatably supported by the housing for rotation about
the axis of the cylinder, and means connected to the cylinder for
selectively rotating the cylinder about its axis relative to the
housing.
5. A pipette assembly in accordance with claim 1 wherein said
spring means controls discharge at a rate defined by the rate of
expansion of the spring means and greater than the rate of
discharge under the effect of gravity.
6. A pipette assembly in accordance with claim 1 wherein said limit
stop means includes an adapter supported by said housing, said
adapter having a plurality of circumferentially spaced recesses on
an end thereof, said adapter surrounding said cylinder, said
cylinder having a limit stop pin adapted to enter each of said
recesses, and means for selectively rotating one of said adapter
and cylinder about the longitudinal axis of the cylinder.
7. A pipette assembly in accordance with claim 1 wherein said
chamber surrounds said rod, a head closing said rod at the end of
the rod remote from said pipette tip support, said sealing means
for sealing the ends of said chamber including a piston connected
to said hollow rod and a seal supported by said cylinder for
movement therewith.
8. A pipette assembly comprising a support housing, a pipette tip
support coupled to said housing, said support having a bore
therethrough, a hollow rod in said housing and communicating with
said bore, a cylinder in said housing surrounding said rod and
spaced therefrom to define a chamber of variable volume, sealing
means between said rod and cylinder for sealing the ends of said
chamber, means defining a passage communicating said chamber with
the interior of said rod, spring means biasing said cylinder away
from said pipette tip support whereby discharge from said pipette
tip is at the rate of expansion of the spring means, and means for
selectively limiting the extent of movement of said cylinder to a
plurality of predetermined distances in a direction along the
longitudinal axis of said cylinder due to the bias of said spring
means.
9. A pipette assembly in accordance with claim 8 wherein said
last-mentioned means includes an adapter supported by said housing
and having a plurality of circumferentially spaced recesses of
different depths, and means for rotating said cylinder about its
longitudinal axis, a limit stop member secured to said cylinder and
adapted to be received in said recesses.
10. A pipette assembly in accordance with claim 8 including a
pipette tip removably mounted on said pipette tip support, said
sealing means including a piston connected to said rod and a seal
supported by said cylinder for movement with the cylinder, said
spring means including a coil spring surrounding said rod.
Description
This invention is directed to a manually operable pipette assembly
which is more accurate than the prior art, reduces mechanical
handling during usage, and increases the efficiency in dispensing
at a constant rate of discharge.
A typical example of the prior art is shown in U. S. Pat. No.
3,290,946 dated Dec. 13, 1966. When the plunger in said patent is
pushed in, it is necessary to keep one's finger over the hole in
the plunger. Thereafter, the plunger is permitted to reciprocate
away from the pipette tip to aspirate liquid into the pipette while
at all times maintaining a finger over the hole of the plunger.
Thereafter, dispensing is attained by removing one's finger from
the hole in the plunger. Thus, the prior art is a three-step
process while relying on finger manipulation and judgment for
accuracy as to the amount of liquid being dispensed.
In the present invention, the number of steps is reduced when using
the pipette assembly while at the same time the operator has the
ability to dispense a predetermined small amount of liquid with
accuracy in excess of 99 percent. Further, the pipette assembly of
the present invention is less expensive and easier to assemble than
some prior art devices. While the pipette assembly has a variety of
uses, it is particularly adapted for use in connection with a blood
coagulation analyzer such as that disclosed in U. S. Pat. No.
3,658,480 dated Apr. 25, 1972 wherein the amount of liquid being
dispensed by the pipette assembly must be accurately
controlled.
It is an object of the present invention to provide a novel pipette
assembly.
It is another object of the present invention to provide a pipette
assembly for accurately dispensing small amounts of liquids.
It is another object of the present invention to provide a pipette
assembly which is easy to assemble and requires fewer steps during
usage.
It is another object of the present invention to provide a pipette
assembly wherein the user may selectively choose one of several
fixed amounts of liquids to be dispensed.
Other objects will appear hereinafter.
For the purpose of illustrating the invention, there is shown in
the drawings a form which is presently preferred; it being
understood, however, that this invention is not limited to the
precise arrangements and instrumentalities shown.
FIG. 1 is a perspective view of a pipette assembly in accordance
with the present invention.
FIG. 2 is a sectional view taken along the line 2--2 in FIG. 1.
FIG. 3 is a sectional view similar to FIG. 2, but illustrating the
components in their relative position when the spring is
compressed.
FIG. 4 is a perspective view of the adapter shown in FIG. 1, but on
a larger scale.
FIG. 5 is a perspective view of the end of the adapter in FIG. 4,
but on a larger scale.
FIG. 6 is a perspective view of the end of the adapter in FIG. 4,
but on a larger scale.
Referring to the drawing in detail, wherein like numerals indicate
like elements, there is shown a pipette assembly in accordance with
the present invention designated generally as 10. The assembly 10
includes a housing 12. Housing 12 is preferably a cylinder of
aluminum, but may be made of other materials and may have other
cross-sections. The housing 12 has first and second ends.
The first end of the housing 12 is provided with threads on its
inner periphery engaged with threads on the outer periphery of a
reduced diameter portion 16 of a pipette support designated
generally as 14. The pipette support 14 is in the form of a nose
with a constantly reducing cross-sectional area from the diameter
of the housing 12 down to the diameter of an axial barrel. The
pipette support 14 is provided with an axial bore 18 therethrough
and terminates at its free end in a reduced diameter portion 20.
The reduced diameter portion 20 is adapted to removably receive an
expendable hollow pipette tip 22. The pipette tip 22 may be a
disposable pipette of high density, rigid polymeric plastic
materials such as polypropylene.
The second end of the housing 12 is closed by means of an adapter
24. The adapter 24 has an end face 25 and a shoulder 26 for contact
with an end of the housing 12. Threads on the ID of said second end
of the housing 12 are engaged with threads on the OD of said
adapter 24. It will be noted that the adapter 24 extends into the
second end of the housing 12 and terminates in a reduced diameter
portion 28 having an axial bore 30.
A hollow rod 32 has one end threadedly coupled to the pipette
support 14. A bore 34 in the rod 32 communicates directly with the
bore 18 and the interior of the pipette tip 22.
A head 36 has a reduced diameter portion telescoped into and
fixedly secured to the other end of hollow rod 32 in any manner
such as by a force fit. A seal 38 is supported by the head 36 and
clamped against the end face of rod 32. Seal 38 will perform the
function of a piston. Thus, rod 32 may be referred to as a piston
rod.
A cylinder 40 is disposed within the housing 12 and surrounds a
portion of the rod 32. Cylinder 40 is spaced from the outer
periphery of rod 32 to define a chamber therebetween designated 46.
Seal 38 engages the ID of cylinder 40 and constitutes a sealing
means for one end of the chamber 46. A cap 42 is connected to the
cylinder 40 in any convenient manner such as by threads. Cap 42
cooperates with a seal 44 which is clamped against an end face of
the cylinder 40. Seal 44 seals the other end of chamber 46. Chamber
46 communicates with the bore 34 by means of one or more passages
48 in the rod 32. The passages 48 are in the nature of bleed
holes.
The cylinder 40 is provided with a limit stop 50 which may take the
form of a radially outwardly directed pin. The reduced diameter
portion 28 on the adapter 24 is provided with circumferentially
spaced recesses 52, 54 and 56, each adapted to selectively receive
the pin 50 and thereby limit the extent of movement of the cylinder
40 in a direction away from the pipette support 14. The depth of
the recesses 52, 54 and 56 is each different.
In a typical embodiment, the depth of the recess 56 is 0.742 inch
and is chosen so as to result in a discharge of 0.2 ml from the
pipette tIp 22. Also, the depth of recess 54 was 0.355 inch to
result in a discharge of 0.1 ml from the pipette tip 22. Also, the
depth of recess 52 was 0.158 inch so as to discharge 0.05 ml from
the pipette tip 22. The depth of the recesses 52-56 and other
related dimensions on other components may be varied as desired to
effect any particular volume of discharge from the pipette tip
22.
In order that the desired volumetric discharge may be selectively
attained, the assembly 10 includes a selector 58 having a reduced
diameter portion telescoped into and fixedly secured to the
cylinder 40 in any desired manner such as a force fit. The selector
58 is provided with a plurality of pointers 60 circumferentially
disposed about the selector 58 and preferably each of a different
color. Each pointer 60 may be selectively aligned with an indicator
point 61 on the end face 25 of the adapter 24. Adapter 24 is
provided with a stepped bearing 62 to facilitate rotational support
of the casing 40 about its longitudinal axis.
The rod 32 is stationary. The cylinder 40. may rotate about its
axis and is also adapted for movement in an axial direction. A
spring 64 surrounds the hollow rod 32. One end of spring 64 engages
a face 66 on the pipette support 14. The other end of spring 64
engages the cap 42 and biases the cylinder 40 in a direction away
from the pipette support 14. In FIG. 3, the spring 64 has been
compressed to its maximum extent, chamber 46 has its maximum
volume, and the selector 58 has contacted the bearing 62. In FIG.
2, the spring 64 has expanded to the extent permitted by entry of
the limit stop 50 into the recess 54.
The pipette assembly may be used as follows: The volume of liquid
to be discharged is first selected by pushing on selector 58 until
limit stop 50 is outside the recesses 52, 54 and 56. Then the
selector 58 is rotated. The pointer 60 may be supplemented with
numerical indicia. When the pointer 60 is aligned with an indicator
61 on the end face 25, limit stop 50 will be aligned with one of
the recesses 52, 54, and 56. Then pressure on selector 58 is
released so that the cylinder 40 reciprocates in an axial
direction, under the bias of spring 64, until the limit stop 50
bottoms out in the selected recess. As shown in FIGS. 4-6, each of
the recesses 52, 54 and 56 is generally V-shaped at least at the
end face of portion 28 to make it easy for the limit stop 50 to
enter its recess and take into consideration that the components
are slightly misaligned.
Thereafter, the assembly 10 is held in a position so that the
pipette tip 22 is immersed in the liquid. Then, the selector 58 is
manually pushed until it bottoms out as shown in FIG. 3. As the
selector 58 and cylinder 40 move in an axial direction, the spring
64 is compressed and the volume of chamber 46 increases by the
selected amount. This creates a suction effect whereby the selected
or desired amount of the liquid is aspirated into the pipette 22.
Thereafter, the assembly 10 is moved to a location wherein the
pipette tip 22 is juxtaposed to the desired receptacle such as a
test tube. The finger pressure applied to the selector 58 may then
be released permitting the spring 64 to expand and effect discharge
from the pipette tip 22 into the receptacle.
As the spring 64 expands, dischrage from pipette tip 22 is at the
rate of expansion of the spring 64. Discharge may be at a constant
rate by using spring 64 in the form of a constant force spring.
Expansion of the spring 64 decreases the volume of chamber 46 and
continues until the limit stop 50 bottoms out in the selected
recess 52, 54 or 56 on the reduced diameter portion 28 of the
adapter 24. Since discharge of the liquid from the pipette tip 22
coincides with expansion of the spring 64, any components of the
liquid are intimately mixed while being discharged and are further
mixed with any liquid in the receptacle.
Since discharge is at the rate of expansion of spring 64, discharge
is at a rate substantially greater than the rate of discharge under
the effect of gravity. Thus, the liquid being discharged is pushed
out of the end of pipette tip 22 by a column of pressurized air in
rod 32 and chamber 46. Hence, discharge need not be in a downward
direction. The assembly 10 has been found to have a volumetric
accuracy of 99.75 percent. Such accuracy is difficult to attain
with prior art devices when dealing with small volumes as described
above.
The entire assembly 10, if desired, may be made from materials so
that it may be sterilized. In the event of an overfill of liquid,
contamination may be prevented by making the cylinder 40, hollow
rod 32, and head 36 from stainless steel. The remaining elements
are preferably made from non-corrosive materials such as aluminum,
brass and the like.
While selection of the amount to be dispensed is preferably
attained by rotating the cylinder 40 relative to adapter 24, it is
within the scope of the invention te attain such selection by
rotating adapter 24 relative to cylinder 40 which would be limited
to axial movement.
The present invention may be embodied in other specific forms
without departing from the spirit or essential attributes thereof
and, accordingly, reference should be made to the appended claims,
rather than to the foregoing specification as indicating the scope
of the invention.
* * * * *