U.S. patent number 3,827,305 [Application Number 05/300,215] was granted by the patent office on 1974-08-06 for adjustable pipette.
Invention is credited to Robert E. Gilson, Warren E. Gilson.
United States Patent |
3,827,305 |
Gilson , et al. |
August 6, 1974 |
ADJUSTABLE PIPETTE
Abstract
An adjustable pipette includes an elongated body defining a
barrel portion and a plunger cavity. A plunger unit is mounted for
reciprocation in the body and includes a plunger portion extending
from the barrel portion into the plunger cavity, and further
includes an operating portion extending rearwardly out of the body.
The plunger unit includes a stop disposed within the barrel
portion, and an adjustable rear stop for varying the volume of a
pipetted sample is carried on a threaded shaft received in a nut
fixed in the body. An indicator including rotatable
indicia-carrying rings is coupled to the shaft for providing an
indication of the volume setting of the pipette. A forward stop for
movement of the plunger unit is provided by an overtravel member
engaged by the plunger stop member. Travel of the plunger unit past
the forward position compresses an overtravel spring, and a seal
assembly is compressed by the overtravel spring into sealing
engagement with the plunger portion of the plunger unit. A sleeve
carried within the threaded shaft around the operating portion of
the plunger unit is adjustable relative to the shaft in order to
align the indicator relative to the shaft. A lock arrangement is
provided for locking the shaft in position to prevent inadvertent
misadjustment of the volume.
Inventors: |
Gilson; Warren E. (Madison,
WI), Gilson; Robert E. (Madison, WI) |
Family
ID: |
23158177 |
Appl.
No.: |
05/300,215 |
Filed: |
October 24, 1972 |
Current U.S.
Class: |
73/864.18;
222/43; 422/925 |
Current CPC
Class: |
B01L
3/0224 (20130101); B01L 2300/026 (20130101) |
Current International
Class: |
B01L
3/02 (20060101); G01n 001/14 () |
Field of
Search: |
;73/425.6,425.4P
;128/234,218F ;141/27 ;222/340,341,43 ;277/102,187 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Queisser; Richard C.
Assistant Examiner: Yasich; Daniel M.
Attorney, Agent or Firm: Mason, Kolehmainen, Rathburn &
Wyss
Claims
What is claimed and desired to be secured by Letters Patent of the
United States is:
1. An adjustable pipette comprising in combination;
an elongated body defining a barrel portion and defining a plunger
cavity adjacent the forward end of said body;
a plunger unit mounted for reciprocation in said body and including
a plunger portion extending from said barrel portion into said
plunger cavity and an operating portion extending rearwardly out of
said body;
first biasing means in said barrel portion urging said plunger unit
in a rearward direction;
said body defining an overtravel chamber disposed between said
barrel portion and said plunger cavity;
a seal assembly resiliently carried in the overtravel chamber in
said body in sealing relation with said plunger portion;
said plunger unit including a stop engaging member permanently
mounted thereon and disposed within said barrel portion;
an overtravel member mounted for movement in said overtravel
chamber and having a forward stop surface engageable by said stop
engaging member upon forward reciprocation of said plunger unit to
a forward stop position;
second biasing means in said overtravel chamber for urging said
overtravel member against the rearward end of said overtravel
chamber;
an internally threaded nut fixed in said body against rotational
and axial movement;
a hollow shaft threaded through said nut for rotational and
reciprocal movement and including a forward end disposed within
said barrel portion and a rear end extending rearwardly out of said
body;
said operating portion of said plunger unit extending through said
shaft;
rear stop means reciprocal with the forward end of said shaft upon
rotation of said shaft in said nut and engageable by said stop
engaging member upon rearward reciprocation of said plunger unit to
a rear stop position; and
indicator means in said body coupled to said shaft for providing an
indication in response to rotation of said shaft indicative of the
position of said rear stop means.
2. The pipette of claim 1, said second biasing means being
substantially stiffer than said first biasing means to provide a
positive feel of the forward stop position.
3. The pipette of claim 1, said overtravel chamber having a forward
wall, said seal assembly being compressed between said second
biasing means and said forward wall around said plunger
portion.
4. The pipette of claim 3, said seal assembly including a retainer
member pressed by said second biasing means toward said forward
wall and having an axial central opening receiving said plunger
portion, a counterbore cavity in the forward side of said retainer
member cooperating with said forward wall to define an annular
chamber surrounding said plunger portion, and compressible seal
means in said annular chamber.
5. The pipette of claim 4, said compressible sealing means
including a flexible cylindrical collar surrounding said plunger
portion, and an O-ring surrounding said collar, said O-ring being
sized to deform when compressed by said second biasing means to
force said collar inwardly against said plunger portion.
6. The pipette of claim 1, a locking member threaded upon said
shaft to the rear of said body, said locking member being
threadable to a locking position against the rear of said body
selectively to lock said shaft against rotation.
7. The pipette of claim 6 including retaining means on said body
and on said locking member for preventing rotation of said locking
member through a complete revolution from the locking position.
8. The pipette of claim 1, said indicator means including a
plurality of indicator rings encircling said threaded shaft within
said body, indicia on said indicator rings, a window means in said
body for viewing of said indicia, one said ring being coupled to
said threaded shaft for rotation therewith while permitting
reciprocal movement of said shaft through said rings, and drive
means coupled between said rings for controlling the relative
movement thereof in response to rotation of said shaft.
9. The pipette of claim 8, said body being formed at least in part
of clear plastic, said window means comprising a region of said
plastic having a polished surface.
10. The pipette of claim 8, the position of said rear stop means
being adjustable relative to said shaft for adjustment of said
rings relative to the rear stop position of said plunger unit.
11. The pipette of claim 10, a cylindrical sleeve slightly longer
than said shaft slidably received within said shaft around said
operating portion of the plunger unit, a head member threaded on
the rearward end of said shaft and engaging the rearward end of
said sleeve, the forward end of said sleeve forming said rear stop
means, and said head being rotatable on said shaft to reciprocate
said sleeve relative to said shaft.
Description
The present invention relates to improvements in adjustable
pipettes.
Traditional pipettes have not been able to meet modern requirements
in that they are not designed rapidly to transfer liquid samples
having precise volumes. As a result many attempts have been made to
provide improved pipetting devices of various constructions which
can conveniently be used to transfer samples rapidly and
accurately. Examples of devices of this type can be found in U.S.
Pat. No. 3,244,009 - Tietje et al. and U.S. Pat. No. 3,506,164 -
Weichselbaum et al.
Although such devices provide samples of precise quantity, they
suffer from several disadvantages. A primary disadvantage is that
such devices are not capable of providing samples of continuously
variable size. At the most, presently available devices are
adjustable by the user between two or a few discrete volumes. In
addition, no clear indication is provided of the volume setting,
and this can result in errors or at least inconvenience in use.
Precise adjustment together with accurate volume indications have
been available in the past with buretting devices. However,
attempts made heretofore to adapt these features to pipettes have
not been sucessful. For example, U.S. Pat. No. 3,013,435 Rodrigues,
Jr. discloses a burette described as capable of being used as a
pipette. Although this device can be continuously adjusted, the
adjustment mechanism is extremely complex and awkward to use.
Moreover, although this device provides an indication useful for
buretting, the indication does not correspond consistently with the
actual volume setting when the device is used for pipetting.
Consequently, the Rodrigues, Jr. device not only would be difficult
or impossible to manufacture but also falls far short of solving
the problems noted above with heretofore proposed pipetting
devices.
Among the important objects of the present invention are to provide
improvements in adjustable pipettes; to provide a pipette having a
simplified and improved arrangement for continuous yet precise
adjustments in volume; to provide a pipette having a reliable,
consistent, and accurate volume indicator; to provide a pipette
wherein the indicator can be aligned relative to the volume
adjustment to assure accuracy; to provide an improved seal assembly
for pipettes; to provide a pipette including structure for locking
the volume adjustment in position; and to provide an improved
adjustable pipette of sturdy and compact construction capable of
economical manufacture.
In brief, an adjustable pipette constructed in accordance with the
present invention includes an elongated body defining a barrel
portion and defining a plunger cavity adjacent the forward end of
the body. A plunger unit is mounted for reciprocation in the body
and includes a plunger portion extending from the barrel portion of
the body into the plunger cavity, together with an operating
portion extending rearwardly out of the body. A seal assembly is
carried by the body and seals against the plunger portion. The
plunger unit includes a stop engaging member mounted on the plunger
unit and disposed within the barrel portion of the body. A forward
stop in the body is engaged by the stop engaging member upon
forward movement of the plunger unit to a forward stop
position.
In order to adjust the sample volume, a hollow threaded shaft
engages a nut fixed in the body and includes a forward end disposed
within the barrel portion of the body and a rear end extending
rearwardly out of the body. A rear stop is associated with the
forward end of the threaded shaft and is engaged by the plunger
unit stop engaging means upon rearward movement of the plunger unit
to a rear position. An indicator arrangement mounted with the body
is keyed to the shaft for providing an indication in response to
rotation of the shaft indicative of the position of the rear stop
and thus of the sample size.
The present invention together with the above and other objects and
advantages may be better understood with reference to the
embodiment of the invention illustrated in the accompanying
drawing, wherein:
FIG. 1 is a partly sectional side view of an adjustable pipette
embodying the features of the present invention;
FIG. 2 is an enlarged, fragmentary sectional view of the adjustable
pipette of FIG. 1 taken along the line 2--2 of FIG. 1;
FIG. 3 is an end view of the adjustable pipette partly taken in
section along the line 3--3 of FIG. 2; and
FIG. 4 is an exploded, fragmentary perspective view of parts of the
seal assembly of the adjustable pipette.
Having reference now to the drawing, there is illustrated an
adjustable pipette generally designated by the reference numeral 10
and constructed in accordance with the principles of the present
invention. The pipette 10 includes a body designated as a whole by
the reference numeral 12 within which there is reciprocably
supported a plunger unit 14. In accordance with one feature of the
invention, there is provided a novel seal assembly generally
designated as 16 providing an air tight seal between the body 12
and the plunger unit 14. A volume adjustment assembly generally
designated as 18 functions in accordance with another feature of
the invention to permit reliable and accurate small-increment
volume adjustments, and volume settings are clearly indicated in
accurate fashion by a volume indicator assembly generally
designated as 20.
Proceeding now to a more detailed description of the structure of
the adjustable pipette 10, the body 12 includes a main housing 22
together with a nose member 24. The main housing 22 defines a
generally cylindrical barrel portion 26 and an enlarged cavity 28
for enclosing the volume indicator assembly 20. The rear end of the
main housing 22 is closed by a cap 30. The cap may be attached in
any suitable manner, and preferably is snapped into place by a
protuberance and notch arrangement 32 (FIG. 2).
Mounting of the nose member 24 to the main housing 22 is
accomplished by means of a nut 34 threaded onto the forward end of
the main housing 22 over the barrel portion 26. The nose member 24
includes an enlarged rearward end section 36 defining an overtravel
chamber 38. A mounting rib 40 is held firmly against the forward
end of the main housing 22 by a flange 42 of nut 34, and a spring
retainer 44 is captured between the rearward end of the nose member
24 and a shoulder 46 defined by a counterbore in the forward end of
the barrel portion 26 of the main housing 22.
Outwardly of the enlarged end 36, the nose member 24 includes an
elongated section 48 defining a plunger cavity 50. In order to
avoid contamination of samples from prior samples, preferably the
forward end of the nose member 24 is provided with frictionally
mounted, tapered tip members such as the member 52 illustrated in
FIG. 1. An opening 54 in the nose member 24 provides communication
between the interior of the tip 52 and the plunger cavity 50. The
interior of the tip 52 is preferably large enough so that entire
samples may be held therein without contact with the nose member
24, and preferably the tip member 52 is made of suitable
non-wetting plastic material to facilitate complete discharge of
samples.
Advantageously, the overall size and configuration of the
adjustable pipette 10 are such as to facilitate its use. The
slender configuration permits insertion of the nose member 24 into
narrow receptacles. The adjustable pipette 10 can readily be held
in the hand, and the main housing 22 is provided with a trigger
guard-type finger handle 56 having a generally C-shape or D-shape
and substantially completely encircling the forefinger of a hand
grasping the main housing 22. The arrangement is such that in use
the adjustable pipette can be held suspended upon a forefinger by
the finger handle 56 in position naturally to be grasped by the
hand with the thumb in position for use over the rearward end of
the pipette 10.
Samples are drawn into and discharged from the tip member 52 by
means of reciprocation of the plunger unit 14 within the body 12.
The plunger unit 14 includes a circular cylindrical plunger portion
60 having a forward end extending into the plunger cavity 50
defined within the nose member 24. Extending rearwardly from the
plunger portion 60, and preferably integral therewith, is an
operating rod portion 62 terminating well outside of the rearward
end of the body 12. A thumb button 64 is attached to the outer end
of the operating rod portion 62 by a screw retainer 66.
In its rest position the plunger unit 14 is urged rearwardly by a
spring 67 (FIG. 2) against an adjustable rear stop, described
hereinafter and comprising part of the volume adjustment assembly
18. The spring 67 is held in compression within the barrel portion
26 of the housing 22 between the spring retainer 44 and a spring
retainer and stop member 68. The member 68 is located over a
shoulder 70 between the plunger portion 60 and operating rod
portion 62 of the plunger unit 14, and is press fit to the plunger
portion 60 or is otherwise permanently attached to form part of the
plunger unit 14. Member 68 is provided with a rearwardly facing
stop surface 72 held against the adjustable rear stop in the rest
position of the plunger.
In order to draw up a sample into the tip member 52, the thumb
button 64 is depressed to move the plunger unit 14 forward. This
movement is accommodated by compression of spring 67. Member 68
includes an elongated small diameter forward end portion 74
comprising a forward stop surface. Forward movement of the plunger
unit 14 results in movement of stop portion 74 through a central
opening 76 in spring retainer 44 until it strikes a forward stop
and overtravel member 78 mounted in the overtravel chamber 38
against the forward side of spring retainer 44. In this position,
the plunger portion 60 of the plunger unit 14 is extended into the
plunger cavity 50. Tip member 52 is immersed in a sample material,
and the thumb button 64 is released. Plunger unit 14 is moved
rearwardly by the force stored in spring 67 to retract the plunger
portion 60 in the plunger cavity 50, and suction within the plunger
cavity 50 communicated to the interior of the tip member 52 draws a
sample of predetermined size into the tip member 52.
In order to discharge the sample from tip member 52, the thumb
button 64 is once again depressed to move the plunger unit 14 in a
forward direction. Upon the discharge stroke, the member 68 again
moves forwardly until surface 74 contacts the forward stop and
overtravel member 78. This member is held in the position
illustrated in FIG. 2 by means of an overtravel spring 80 held in
compression between the forward side of member 78 and the rearward
side of a spring retainer and pressure member 82 disposed at the
forward end of the overtravel chamber 38. During a discharge
stroke, the plunger unit 14 is moved through an overtravel movement
wherein the forward stop portion 74 of the member 68 drives the
forward stop and overtravel member 78 against the force of the
spring 80 into the overtravel chamber 38. As a result of this
overtravel movement the plunger portion 14 moves further into the
overtravel chamber 50 during the discharge stroke than during the
intake stroke. Thus, it is assured that the entire sample is fully
discharged from the tip 52. In order to provide a positive, easily
detected stop at the end of the intake movement, the spring 80 is
preferably substantially stiffer than the spring 67.
In accordance with a feature of the invention, the seal assembly 16
of novel construction provides a reliable, airtight, low friction
seal between the body 12 and the plunger unit 14. Moreover, seal
assembly 16 is spring loaded by over-travel spring 80 and thus
spring 80 performs a dual function.
More specifically, as shown in FIGS. 2 and 4, the seal assembly 16
includes a toric seal member 86 disposed within a counterbore
cavity 88 in the forward end of the spring retainer and pressure
member 82. Seal member 86 includes a cylindrical collar portion 90
intimately encircling the plunger portion 60 and a flange section
92 engaged by the member 82. A resilient O-ring 94 is held around
the collar 90 between the flange 92 of the seal member and the
forward wall of the overtravel cavity 38. The size of the O-ring 94
relative to the size of the toric seal member 86 and cavity 88 is
such that the O-ring 94 is somewhat compressed by the force of the
spring 80. The toric seal member is of somewhat soft and flexible
plastic material, and the cylindrical collar portion 90 of the seal
member 88 is resiliently forced by the spring loaded O-ring 94
inwardly into sealing relation with the plunger portion 60. The use
of a smooth metal plunger unit 14 and of a flexible plastic seal
member 86 assures not only a good seal, but also very low sliding
friction during reciprocation of the plunger unit 14.
An important advantage of the adjustable pipette 10 of the present
invention is that it can be easily adjusted in a continuously
variable manner and with great precision and accuracy. The volume
adjustment assembly 18 provided in accordance with the present
invention includes a hollow threaded shaft 100 having an inner end
disposed within the barrel portion 26 of the housing 22 and having
an outer end spaced outwardly of the cap 30. The shaft 100 is
received in an internally threaded nut member 102 fixed against
rotational and longitudinal movement by means of a locking pin 104.
Nut 102 is received in the rearward end of the barrel portion 26
and includes a flange 106 received in the forward end of the
enlarged cavity 28. A retaining nut 108 is threaded onto the
innermost end of the shaft 100 and is then locked in place, as by
deformation. The purpose of the retaining nut 108 is to prevent the
shaft 100 from being inadvertently withdrawn through the nut member
102.
Rotation of the shaft 100 is facilitated by the provision of a
knurled head or cap 110 threaded over the outer end of the shaft
100 and locked into position by means of a pair of screw retainers
112. Slidably received over the operating rod portion 62 of the
plunger unit 14 within the hollow threaded shaft 100 is an inner
sleeve or shaft 114. The purpose of sleeve 114, described more
fully hereinafter, is to permit adjustment of the volume indicator
assembly 20 in relation to the volume adjustment assembly 18. The
forward end of the sleeve 114, designated by the reference numeral
116, extends slightly beyond the forward end of the threaded shaft
100 and forms the forwardmost part of the volume adjustment
assembly 18. Thus the forward end 116 of sleeve 114 is engaged by
the stop surface 72 of the member 68 and provides the rearward stop
for motion of the plunger unit 14.
Adjustment of the sample volume of pipette 10 is accomplished by
rotation of the head 110 resulting in reciprocation of the threaded
shaft 100 and of the sleeve 114 due to threaded engagement with the
nut member 102. This reciprocation moves the rearward stop 116
toward and away from the forward stop 78 thus adjusting the stroke
of the plunger member 14 and the volume of a sample.
The volume adjustment assembly 18 also includes provision for
locking the unit in position for any desired sample size. For this
purpose there is provided a locking ring 118 threaded upon the
shaft 100 to the rear of the cap 30 of the main housing 22. Once
the shaft has been rotated to position it in the desired
longitudinal position, the locking ring 118 is threaded inwardly
firmly against the cap 30 thus locking the shaft 100 against
further rotation.
In order to prevent movement of the locking ring 118 more than a
slight distance away from the cap 30, there is provided a retaining
pin 120 extending outwardly from cap 30 into a circular groove 122
in the underside of locking ring 118. If an attempt is made to
unscrew the locking ring 118 away from the cap 30, the retaining
pin 120 is engaged as illustrated in FIGS. 2 and 3 by a stop pin
124 extending across the groove 122 in a radial direction. The
arrangement is such that rotation of the locking ring 118 in the
opposite direction away from the position illustrated in FIG. 3
will result in tightening of the ring 118 against the cap 30 in
less than a full revolution.
In accordance with another feature of the invention, the volume
indicator assembly 20 provides an exact and easily perceived
readout of the volume setting of the volume adjustment assembly 18.
Arranged in stacked relationship within the enlarged cavity 28
between cap 30 and flange 106 are a series of indicator rings 130,
132 and 134, each encircling the adjustment shaft 100. In the
illustrated embodiment of the invention the rings 130, 132 and 134
express the volume setting in units, tens and hundreds,
respectively, of microliters. It will be understood that fewer or
more rings graduated in any desired units may be provided.
In order to couple the indicator assembly 20 with the volume
adjustment assembly 18, the threaded shaft 100 includes a groove
136 extending throughout its length. The units ring 130 includes an
inwardly extending projection 138 received in the groove 136 to the
end that the ring 130 rotates with the shaft 100 but permits the
shaft 100 to move longitudinally relative to the ring. The tens
ring 132 and the hundreds ring 134 are free for relative rotation
independent of the threaded shaft 100.
Movement of the rings 130, 132 and 134 relative to one another is
accomplished in a conventional manner. As a result of one full
revolution of the units ring 130, a single pair of gear teeth 140
engage a spur gear 142 mounted on a shaft 144 extending axially
through the length of the enlarged cavity 28 of the housing 22. The
spur gear 142 engages continuous gears 146 on the tens ring 132 in
order to move it a single increment of a tenth of a revolution.
Similarly, each full rotation of the tens ring 132 results in
incremental movement of the hundreds ring 134 by virtue of a single
pair of gear teeth 148, an additional spur gear 150 and continuous
gear teeth 152 on the hundreds ring 134.
As appears in FIG. 1, there is provided a transparent window 154
for viewing of the indicator rings 130, 132 and 134. Preferably the
entire main housing 22 is formed of clear plastic with the window
area 154 being polished for clear visibility. Any other window
structure may be used if desired. Each of the rings 130, 132 and
134 is provided with numerical indicia, and if desired the units
ring 130 may be provided with fractional graduations registering
with an index line 156 on the window 154.
In order to assure accuracy of the indication provided by the
assembly 20, there is provided a zero adjustment feature. In the
initial fabrication and assembly of the pipette 10, the rings 130,
132 and 134 are mounted so that a zero indication appears when the
shaft 100 is threaded inwardly approximately until the stop portion
74 is in contact with the forward stop 78 in its rearward position.
In order precisely to adjust the zero position, the funtion of the
sleeve 114 comes into play. The head 110 is rotated until the
indicator assembly 20 provides precisely a zero indication. At this
point the screw retainers 112 are loosened and the head 110 can be
rotated while the shaft 100 remains stationary. During such
rotation the reading of the indicator 20 is not changed. However,
rotation of the head 110 advances or retracts the sleeve 114
relative to shaft 100 to precisely locate the plunger assembly 14
at the zero volume position. When this position has been reached,
the screw retainers 112 are tightened once agin and the zero
adjustment is completed.
The operation of the adjustable pipette 10 will be apparent to
those skilled in the art in light of the above detailed
description. In use, the pipette is first adjusted through
manipulation of the volume adjustment assembly 18 to the desired
volume. This is accomplished by rotation of the head 110 to cause
reciprocation of the shaft 100 thus setting the position of the
rear stop 116. When the desired volume as appearing at the window
154 has been attained, the locking ring 118 is rotated firmly
against the cap 30 in order to prevent further inadvertent rotation
of the shaft 100.
To draw up a sample, the thumb button 64 is depressed to drive the
plunger portion 60 of the plunger unit 14 forwardly into the
plunger cavity 50 through a precisely predetermined distance until
the stop portion 74 strikes the forward stop 78. Inadvertent
overtravel is avoided due to the stiffness of the overtravel spring
80. At this point the tip member 52 is immersed in a sample
material and the thumb button 64 is retracted to draw up the
sample.
The sample is discharged by once again depressing the thumb button
64 to move the plunger portion 60 into the plunger cavity 50.
During the discharge stroke the plunger unit 14 is moved into the
overtravel range by forcing the forward stop and overtravel member
78 forwardly into the overtravel chamber 38 against the force of
the stiff spring 80. This overtravel movement assures complete
discharge of the sample. When the thumb button 64 is released, the
plunger unit 14 returns to its rest position with the surface 72
against the rear stop 116.
Although the invention has been described with reference to details
of the illustrated embodiment, it should be understood that such
details do not limit the invention which is defined in the appended
claims.
* * * * *