U.S. patent number 3,615,240 [Application Number 05/013,779] was granted by the patent office on 1971-10-26 for micropipette comprising a pawl mechanism for driving a rotary member.
This patent grant is currently assigned to Micromedic Systems. Invention is credited to Manuel Claude Sanz.
United States Patent |
3,615,240 |
Sanz |
October 26, 1971 |
MICROPIPETTE COMPRISING A PAWL MECHANISM FOR DRIVING A ROTARY
MEMBER
Abstract
A device for drawing and distribution of liquid, as exemplified
in a pipette, operated alternately in two directions, for drawing
and distributing liquid, having an enclosure for the liquid storing
purposes, comprising a pawl mechanism for driving a rotary member,
an armature rotatably mounted around the rotary member, a support
on the armature for pivotal movement at right angles to the
rotational axis of the armature, first and second pawls secured to
opposite sides of the support axis, and capable of being
selectively brought into engagement with the teeth of the rotary
member by rocking the support in one direction in the case of the
first pawl, and in the opposite direction in the case of the second
pawl.
Inventors: |
Sanz; Manuel Claude (N/A,
CH) |
Assignee: |
Systems; Micromedic
(PA)
|
Family
ID: |
4243299 |
Appl.
No.: |
05/013,779 |
Filed: |
February 24, 1970 |
Foreign Application Priority Data
|
|
|
|
|
Feb 26, 1969 [CH] |
|
|
2864/69 |
|
Current U.S.
Class: |
73/864.13;
73/864.18; 222/282; 222/309; 422/515 |
Current CPC
Class: |
F16H
31/001 (20130101); B01L 3/0217 (20130101) |
Current International
Class: |
F16H
31/00 (20060101); B01L 3/02 (20060101); G01N
001/00 (); G01N 001/14 () |
Field of
Search: |
;23/253,259,292
;222/282,295,309 ;73/425.4P,425.6 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Wolk; Morris O.
Assistant Examiner: Serwin; R. E.
Claims
I claim:
1. An analytical pipette for aspirating and discharging
predetermined minute amounts of liquid, comprising housing means,
chamber means within said housing means, piston means mounted in
said housing means for axial movement therein and adapted to
cooperate with said chamber means to produce either a vacuum or
compression, means associated with said piston means in said
housing means to prevent rotary movement of said piston means,
cylinder means mounted for rotary movement within said housing,
gear means connecting said piston means with said cylinder means
for translating the rotary motion of said cylinder means into axial
movement of said piston, means to rotate said cylinder means in
either of two directions, a first adjustment means to limit the
rotation of said cylinder means in a first direction, a second
adjustment means to limit the rotation of said cylinder means in a
second direction, whereby the amount of aspiration and compression
can be preset by said first and second adjustment means.
2. An analytical pipette as in claim 1, wherein there are indicia
and indicator means associated with said first and second
adjustment means and said means for rotating said cylinder means,
whereby the amount of aspiration and discharge can be accurately
preset.
3. An analytical pipette as in claim 1, wherein said cylinder means
surrounds said piston means and a portion thereof forms a guide for
said piston means, said gear means comprising an external threaded
section on said piston means and mating internal threads on said
cylinder means.
4. An analytical pipette as in claim 1, wherein said chamber means
comprises a tube secured to the end of said housing and said piston
means comprises a body portion and rod extending therefrom, said
rod extending into said tubing.
5. An analytical pipette as in claim 1, wherein the means to rotate
said cylinder includes at least one disk mounted to said cylinder
and having teeth around its circumference, support means
surrounding said piston means, said support means having two pawls,
linkage means connecting said means to rotate said cylinder means
with said support means and adapted to alternatively engage each of
said pawls on said toothed disk to rotate said cylinder means in
alternate directions.
6. An analytical pipette as in claim 5, wherein said linkage means
includes an armature surrounding said support means and mounted for
rotative movement in said housing, braking means for decelerating
said armature during rotation thereof, said support means hinged to
said armature means, said pawls being attached to said support
means on each side of its hinged axis and adapted to alternately
engage said toothed disk upon pivoting of said support means, stop
means for limiting the amount of pivot of said support means, and a
force applying member connecting said support means with said means
to rotate said cylinder.
7. An analytical pipette as in claim 6, wherein said means to
rotate said cylinder comprises a ring surrounding said housing
means and mounted for rotary movement thereon.
8. An analytical pipette as in claim 6, wherein said housing means
is cylindrical and said armature is of a cylindrical
configuration.
9. An analytical pipette as in claim 8, wherein said cylindrical
armature is square C-shaped in cross section and said support means
is circular and is pivoted within a channel formed by the C-shape
of said armature.
10. An analytical pipette as in claim 9, wherein said force
applying means is a stem, said stem being connected to said support
means at a point diametrically opposite its hinge axis.
11. An analytical pipette as in claim 10, wherein said braking
means consists of at least one resilient member on said housing
means abutting said armature means.
12. An analytical pipette as in claim 6, wherein there is a stop
means mounted on said housing to limit the maximum angular
displacement of said armature relative to said housing.
13. An analytical pipette as in claim 12, wherein said stop means
consists of a stop member secured to said housing means, an
aperture in said armature means, said stop member projecting
through said aperture, and two pins mounted in said armature,
whereby said stop member engages said pins to limit the angular
displacement of said armature.
14. An analytical pipette as in claim 6, wherein said first and
second adjustment means comprise two cams mounted on each side of
said armature, each cam having two internal arcuate cam surfaces,
said surfaces having a profile formed by concentric arcs, the
larger radius arc forming the smaller cam surface, the radii
differing by an amount greater than the depth of penetration of
either pawl in the teeth of said disk, two pins on said support
means parallel to its axis of rotation and extending in opposite
directions, each adapted to cooperate with a separate cam, the
location of said pins on said support means being such that when
both pins are in contact with the smaller radius cam surface of
their respective cams, the support means is in a centered or
neutral position with neither pawl engaging said toothed disks.
15. An analytical pipette as in claim 14, wherein each cam has a
force-applying member connecting it to an adjustment ring, said
adjustment ring being circular and mounted for rotary movement on
the external surface of said housing, indicia and indicator means
associated with each said adjustment ring so that an accurate
setting can be made after predetermining the desired amount of
aspiration or discharge or both, one of said adjustment rings
adapted to limit the maximum amount of aspiration and the other
adapted to limit the maximum amount of discharge.
16. An analytical pipette as in claim 15, wherein said armature has
a square C-shaped cross section, apertures in the top and bottom
flanges respectively of said C-shaped armature to allow said pins
to extend to said cam surfaces, the size of each aperture being
sufficient to allow pivoting of said support means and engagement
of said disk and one of said pawls when the rotation of said
cylindrical means commences in one direction.
17. An analytical pipette as in claim 1, including limiting means
to limit the maximum axial travel of said piston means.
18. An analytical pipette as in claim 1, wherein the means to
prevent rotary movement of said piston means consists of a stud in
slot means.
19. An analytical pipette as in claim 1, including a frame means,
said frame means having clamp means engaging said housing means, a
toothed ring gear on said cylinder means, a manually manipulatable
means on said frame means including a friction clutch adapted to
engage and drive said cylinder.
20. An adjustment mechanism for an analytical liquid drawing and
distributing instrument, said mechanism comprising:
a. an axially movable member, and
b. a rotatable member, and
c. motion-translating means connecting said axially moveable and
rotatable members to translate the rotary motion of said rotatable
member into axial motion of said movable member, and
d. pivot means adapted to rotate said rotatable member, and
e. a first pivotable means adapted to adjustably limit the degree
of rotation of said rotatable member in a first angular direction,
and
f. a second pivotable means adapted to adjustably limit the degree
of rotation of said rotatable member in a second angular direction,
both said pivotable means mechanically connected to said pivot
means, whereby the amount of rotation of said rotatable member can
be preset for either direction of rotation.
21. An adjustment mechanism as in claim 20, further including:
h. indicia and indicator means associated with said pivot means and
each of said pivotable means for accurately presetting the limits
of the angular movement of said rotatable member.
22. An adjustment mechanism as in claim 20, wherein said rotatable
member surrounds said axially movable member and is adapted to act
as a guide therefor, said motion translating means comprising
portions of the rotatable member and the axially movable member
having mating engaging threads.
23. An adjustment mechanism as in claim 20, further including:
h. at least one toothed disk connected to said rotatable member,
and
i. ring means surrounding said disk, and
j. a freely rotatable armature surrounding said ring means and
having an inwardly opening channel, and
k. said ring means pivoted inside of said channel, and
l. two pawls on said ring means on the inner circumference thereof,
and
m. stem means connecting said ring means and said pivot means,
and
n. stop means limiting the degree of rotation of said armature
means to a predetermined maximum whereby said pawls alternately
engage said toothed disks to engage said rotatable member upon
pivoting of said ring means upon movement of said pivot.
24. An adjustment mechanism as in claim 23, wherein said pivotable
means have inner cam surfaces adapted to cooperate with a portion
of said ring means to limit the degree of rotation of said armature
within the maximum rotation allowed by said stop means.
25. An adjustment mechanism as in claim 20, further including:
h. a stop means setting the maximum amount of travel of said
rotatable member, and
i. cam means associated with both said pivotable means to limit the
amount of rotation of said rotatable member within the maximum
limits set by the stop member.
Description
This invention relates to a pawl mechanism for driving a rotary
member.
In very many fields of science or technology it is necessary to be
able to take up or deliver particularly small quantities of liquid,
for example of the order of one nanoliter.
This is particularly the case in biology, for example when it is
required to tap kidneys, in particular the kidney tubules, or in
chemistry, in the field of chromatography in the gaseous phase in
order to effect the injection of microquantities of liquid.
In certain micromechanisms such as, for example, those of watch
parts, it is also required, to effect lubrication by the
distribution of oil in particularly small quantities, and in an
identical manner and in as accurate a manner as possible during
each such lubricating operation.
These intake and delivery operations are at present effected by all
sorts of pipettes in which the volume aspirated or discharged
depends to a fairly large extent on the viscosity of the liquid
being taken up or delivered, and on the duration of these
operations.
An object of the invention is to obviate the above-mentioned
disadvantage by devising a mechanism which will effect simple and
rapid manipulation of a pipette of very high accuracy and capable
of dealing with quantities of liquid of the order of one
nanoliter.
According to the invention there is provided a pawl mechanism for
driving a rotary member which comprises a toothed wheel
kinematically connected to said member, an armature rotatably
mounted around said member coaxially with the rotational axis of
the latter, a support mounted on the armature for pivotal movement
at right angles to the rotational axis of the armature and
enveloping said toothed wheel at least over a part of its
periphery, first and second pawls secured to the support on
opposite sides of its pivotal axis, in line with said toothed
wheel, and capable of being selectively brought into engagement
with the teeth of the wheel by rocking the support in one direction
in the case of the first pawl and in the opposite direction in the
case of the second pawl, and which further comprises a brake for
braking the rotary motion of the armature, a support bearing on the
armature for limiting said rocking in each direction, and a member
rigid with the support to enable the necessary couple to be
transmitted to the mechanism firstly for rocking said support
relative to the armature in one or the other direction, into a
position of engagement of one of said pawls with said toothed
wheel, and secondly for angularly driving the armature against the
action of the brake after the support has come to bear on the
armature, and hence for angularly driving the rotary member by the
thrust exerted by the pawl on the toothed wheel.
In the accompanying drawings:
FIG. 1 is a longitudinal section through a pipette for the intake
and delivery of liquid which is fitted with one form of embodiment
of a pawl mechanism according to the invention;
FIG. 1a shows a detail of FIG. 1 on a larger scale;
FIG. 2 is a cross section of the pipette along the line II--II of
FIG. 1;
FIG. 3 is a section through part of the FIG. 1 pipette, taken along
the line III--III of FIG. 2;
FIG. 4 is a perspective view of a component of the FIG. 1
pipette;
FIG. 5 is a side view showing part of the casing for the FIG. 1
pipette;
FIG. 6 is a diagrammatic cross section of the pipette along the
line VI--VI of FIG. 5;
FIGS. 7 to 9 ARE CROSS SECTIONS OF THE PIPETTE ALONG THE LINE
II--II of FIG. 1 in three different positions of certain
components;
FIGS. 10, 11, 11a, 12 and 13 illustrate diagrammatically various
ways in which of the pawl mechanism fitted in the FIG. 1 pipette
can operate; and
FIGS. 14 and 15 represent respectively a front elevational view and
a plan view of the FIG. 1 pipette mounted on a support device
serving to fill the pipette.
The illustrated pipette comprises a tubular handle 1 at the top end
of which is arranged a head 2 carrying firstly, three rotary rings
3, 4 and 5 and secondly, a mounting 6 for a cranked tube 7 by means
of which the intake of liquid and its delivery can be effected.
This intake and delivery are controlled by rotational movement of
the ring 4, in one direction for intake and in the opposite
direction for delivery, the quantity of liquid which can be
aspirated into or discharged from the tube being set beforehand in
particularly accurate manner by suitably positioning the rings 3
and 5 relative to associated fixed reference points 8a and 8b (FIG.
15). For this purpose, the rings 3 and 5 respectively carry on
their outer surfaces equidistant graduations 3a and 5a in facing
relationship with the reference points 8a and 8b, each graduation
corresponding, in the illustrated pipette, to a difference in
aspirated or discharged volume of 5 nanoliters with respect to the
adjacent graduations.
The handle 1 is formed by a metal sleeve 9 which is covered with a
sheath 10 of plastics material and which is closed off at one end
by a cap 11 secured to the sleeve by screwing while the other end
is rigid with a cup 12 forming, in cooperation with a cap 13
screwed on the cup, the casing of the head 2.
Within the sleeve 9 and the casing of the pipette head 2 is
arranged an axially movable shaft 14 having an annular flange 14a
which is slidably mounted in an enlarged diameter portion 9a of the
sleeve and which also forms a stop member for limiting movement of
the shaft 14 in direction F.sub.1 by abutment against a shoulder 9b
of the sleeve, the amplitude of possible displacement of the shaft
in direction F.sub.2, opposite to F.sub.2, opposite to F.sub.1,
being limited by abutment of the end of a shaft portion 14b
adjacent flange 14a with the internal surface of the cap 11.
On the side of flange 14a opposite to portion 14b, the shaft 14 has
a cylindrical portion 14c whose length corresponds at least to the
extend to which the shaft can travel axially from the moment it
moves away from the shoulder 9b until its portion 14b comes into
contact with the cap 11, or vice versa; this cylindrical portion is
formed with a longitudinal groove 14d within which is freely
engaged the tip of a stud 9c which projects into the bore of sleeve
9 and prevents any rotary displacement of shaft 14 during axial
sliding movement thereof.
This cylindrical portion 14c of the shaft is extended by a threaded
part 14c with which engages a nut 15a formed at one end of a sleeve
15, the other end 15b of this sleeve constituting a bearing for
guiding a cylindrical shaft portion 14f adjacent the threaded
portion 14e, during axial movement of the shaft.
The shaft 14 terminates in a cylindrical element 14g of lesser
diameter than the portion 14f and from the end face of which
projects a rod 14h engaged, at its free end, in the tube 7, in
particular in the tube portion 7a held by the mounting 6 in coaxial
relationship with the rod 14h. The diameter of rod 14h is so sized
as to slide with a fairly close fit in the tube portion 7a when the
shaft 14, of which rod 14h forms part, is moved axially. When so
sliding, the rod 14h plays the part of a pump piston with the tube
portion 7a acting as the cylinder, and it is this rod which causes
liquid to be sucked into the tube, upon movement of the shaft in
direction F.sub.2, and the liquid filling the tube to be discharged
therefrom, upon movement of the shaft in the opposite direction
F.sub.1.
It should at this point be noted that the tube 7 is secured in a
fluidtight manner on the cap 13 by the mounting 6, which mounting
comprises a nut 6a engaging over a threaded flange 13a that extends
radially from the cap 13, and serving to press a ring 6b towards
the cap 13 inside the annular flange 13a. at one end of ring 6b is
formed a cylindrical aperture portion in which is engaged a sleeve
of synthetic material 6c, passing through the nut 6a via a passage
6c and surrounding the tube portion 7a over part of its length,
this sleeve constituting a resistant protective element for the
tube. At its other end, the ring is formed with a frustoconical
aperture portion adapted to fit over an annular gasket 6e of
synthetic material, arranged around the base of tube 7, in contact
with the cap 13. The outer surface of gasket 6e is also of
frustoconical shape so that upon nut 6a being tightened gasket 6e
is clamped by ring 6b thereby firmly to hold tube 7 in position.
Another annular gasket, 6f, is located in a recess 13b in cap
13.
Because the shaft 14 is prevented from rotating about itself by
virtue of the stud 9c engaging in groove 14d, any rotation of
sleeve 15, and thus of nut 15a, is converted into a displacement of
the shaft in direction F.sub.1 or F.sub.2 depending on the
direction of rotation of sleeve 15. This rotation is caused by
rotatably moving the ring 4 to an extend which can be adjusted by
acting on rings 3 and 5 as will now be described.
The sleeve 15 is in fact rotatably mounted with respect to the cup
12 firstly by virtue of a first ball and cage assembly 16 mounted
between a flange 15c on the sleeve and a shoulder 12a provided in
the base of this cup, and secondly by virtue of a second ball and
cage assembly 17 arranged between two rings 18a and 18b of which
the first, 18a is force-fitted in part in an annular member 19 of
synthetic material, and of which the second, 18b, is mounted with
light frictional engagement on the portion 15b of sleeve 15 and is
subjected to the action of a spring washer 20 urging it against the
ball and cage assembly 17. The annular member 19 is fitted into the
part of the cup 12 adjacent the mouth of the latter, and its
aperture 19a is sized to correspond to the external diameter of the
sleeve portion 15b. The member 19 thus acts firstly, as a
positioning member for sleeve 15 in the cup 12 of the pipette head
2, and therefore also as a positioning member for shaft 14 via said
sleeve, and secondly, as a rotation bearing for sleeve 15.
The spring washer 20 bears on a toothed disc 21 which is
forcefitted, together with a second similar toothed disc 22, on the
external surface of sleeve portion 15b, the second disc bearing on
a shoulder 15d of said sleeve.
The dimensions and arrangement of the members 17 to 22 are such
that the toothed discs 21 and 22 come to lie symmetrically on
opposite sides of the sectional plane II--II that divides the ring
4 into equal parts.
As can be seen from FIG. 2, the teeth of discs 21 and 22 are saw
toothed in shape, the teeth of one disc being however directed in a
direction opposite to those of the other.
These discs constitute in fact ratchet wheels with which cooperate
a pawl 23 in the case of disc 21 and a pawl 24 in the case of disc
22 (FIGS. 2 and 3), which pawls project from the inner face of a
ring 25 in diametrically opposite positions. The ring 25 is pivoted
on a pin 26 between the two radial flanges of an annular armature
27 which is of U-shaped section and which is rotatably mounted in
the cup 12, its peripheral portion, which constitutes the base of
the U, sliding over the inner surface of the cup. The extent to
which the armature 27 can rotate is limited by the engagement of
the tip of a screw 28 extending between the armature flanges,
through a peripheral slot 27a, with either of two dowels 29a and
29b mounted between these flanges, symmetrically on opposite sides
of the pin 26 (FIGS. 1 and 2).
The ring 25 has, in the vicinity of pawl 23, a peg 30 and, in the
vicinity of pawl 24, a peg 31, these pegs extending in opposite
directions through circular ports 27b and 27c (FIGS. 2, 3 and 6)
respectively formed in the radial flanges of armature 27.
The diameter of these ports is such that, whenever pawl 23 or 24 is
brought into engagement with the associated wheel 21 or 22 by
pivoting ring 25 about its pin 26, pegs 30 and 31 come to bear
against the edges of ports 27b and 27c, i.e. the left-hand side of
these edges (FIG. 6) when pawl 23 cooperates with wheel 21 or the
right-hand side of these edges when pawl 24 engages with the teeth
of wheel 22. This contact of pegs 30 and 31 with the edges of ports
27b and 27c determines the extent to which the pawls 23 and 24
penetrate between the teeth of the associated toothed disc: in
fact, this penetration is never total for the pawl that is in
engagement, whereas the other pawl is at that moment totally out of
engagement with the teeth of its associated disc.
The armature 27 is additionally formed, in the part thereof
opposite pin 26, with a peripheral slot 27d through which passes a
stud 25a rigid with ring 25 (FIGS. 1, 2 and 6). This slot 27d has a
length sufficient to enable ring 25 to pivot about pin 26 to the
extent indicated above, without rod 25a coming into engagement with
armature 27.
In the sidewall of cup 12 are formed three slots 123, 124 and 125
which have parallel edges and which have coinciding and equal
arcuate lengths corresponding substantially to the angular distance
between the dowels 29a and 29b plus the angular distance, as viewed
from the axis of the cup 12, travelled by the stud 25a of ring 25
when the latter is pivoted about pin 26, which pivotal movement is
limited by the pegs 30 and 31 coming into contact with the edges of
ports 27b and 27c. These slots are contained in equidistant and
parallel planes that are transverse to the longitudinal axis of the
cup; a slot 126, perpendicular to the slots 123, 124 and 125,
connects the central parts of the latter and the edge of cup 12.
The slots 123, 124, 125 and 126 lie below the rings 3, 4 and 5 and
below the cap 13 and are therefore not visible when the pipette is
in the assembled state.
These slots define in the sidewall of the cup 12 four tonguelike
12A, 12B, 12C and 12D (FIG. 5) which are arranged in facing pairs,
12A and 12C, and 12B and 12D, and which are slightly bent, before
assembly, in the direction of the axis of cup 12 in such a way as
to exert a slight pressure on the armature 27 (FIG. 6), thereby
causing a braking action on the armature when the latter is rotated
in the cup, in either direction.
It should at this point be indicated how the rings 3, 4 and 5 are
mounted on the sidewall of cup 12.
The ring 5 is maintained in engagement with a shoulder 12b of the
cup by a ring 8B (FIGS. 1 and 3) which carries the reference point
8b and which is angularly locked by a screw, not shown, engaging
with the cup.
Opposite this ring 8B is a similar ring 8A which carries the
reference point 8a and which is angularly locked by a screw, also
not shown and rigid with the cup, this ring 8A being separated from
ring 8B by an intermediate ring 8C locked angularly by the screw 28
and by two other screws 28a and 28b.
These rings 8A and 8B moreover form a support for the rotating ring
4 which is in addition locked axially between the rings 8A and 8B
by engagement of an internal portion 4a between their opposite
faces (FIGS. 1 and 3).
The ring 3, which bears on ring 8A (FIGS. 1 and 3), is held in
position on the cup 12 by the cap 13.
To each of the graduations 3a and 5a on the rotary rings 3 and 5,
there corresponds on the fixed rings 8A and 8B a hemispherical
recess 32 made in the faces of these rings opposite their
associated rotary rings 3 and 5 (FIG. 1a); the recesses in in each
series are equidistantly arranged over an arc of a circle and are
adapted to cooperate with a microball 33 subjected to a spring 35
and slidably mounted in a corresponding recess 34 formed in both of
the rings 3 and 5 opposite the median points of the graduations 3a
and 5a. The two series of recesses 32 provided in rings 8A and 8B
ensure exact positioning of each graduation on rings 3 and 5
opposite the corresponding reference point 8a or 8b by penetration
of the corresponding microball 33 into the appropriate one of the
corresponding series of recesses 32.
The ring 8C is slotted at 80 in the part thereof facing the slot
124, over an angular length corresponding to that of said slot
(FIGS. 1 and 2).
The stud 25a which is rigid with ring 25 and which extends not only
through the slot 27d of armature 27 but also through the slot 80 of
ring 8C and the slot 124 of cup 12, projects into a recess 4b of
ring 4 with which it is therefore in engagement.
It follows that any rotary displacement imparted to the ring 4
causes stud 25a as well as ring 25 and armature 27 to be driven in
the same direction, the extent of the displacement of ring 4 being
limited by the abutment of the projecting tip of screw 28 against
one or other of the dowels 29a and 29b.
The diameter of this projecting tip is the determining factor for
exactly adjusting the maximum amount of liquid the pipette can
aspirate or discharge during a single actuation of ring 4. This
quantity depends on the axial distance travelled by the rod 14h of
shaft 14 within the portion 7a of tube 7, such distance being
directly related to the angular displacement of the nut 15a, i.e.
of the sleeve 15 carrying the toothed discs 21 and 22. The drive of
armature 27 and of ring 25 carrying pawls 23 and 24, by means of
which discs 21 and 22 are rotated, is dependent on the ring 4,
FIGS. 7 and 8 show the way in which these discs are rotated.
In FIG. 7, which is a view similar to that of FIG. 2 but with the
cup 12 and the ring 8 shifted angularly through 90.degree. in an
anticlockwise direction, the ring 4 has been moved to an extreme
left position such that the dowel 29a of armature 27 contacts the
tip of stop screw 28, ring 25 being pivoted about pin 26 into a
position in which pawl 23 comes into engagement with the teeth of
disc 21 whereas pawl 24 is disengaged from disc 22.
When ring 4 is turned in direction F.sub.3 (FIG. 7) it is only ring
25 which is at first caused to move, by pivoting about pin 26,
because the armature 27 is held in place by the braking action
which is exerted on its outside surface by the tonguelike elements
12A, 12B, 12C and 12D of cup 12. The extent to which the ring 25
can pivot is governed by the size of the ports 27b and 27c which
are formed in armature 27 and in which are engaged pegs 30 and 31.
Thus the ring 25 will pivot for as long as the pegs, upon moving
away from the edge portions of the ports with which they are in
contact, as shown, say, in FIG. 7, do not come into contact with
another portion of the port edges situated approximately
diametrically opposite the first portion, as shown, say, in FIG. 8.
The pawl 24 of ring 25 will then mesh with the toothed disc 22
whereas pawl 23 will then be remote from the disc 21 with which is
meshed previously.
It is upon completion of this changeover and upon continued
rotation of the ring 4 in direction E.sub.3, that the sleeve 15
comes to be turned by the pawl 24 which is now in meshing
engagement with disc 22. Thus, because the ring 25 can no longer
pivot within armature 27 as it is abutting against the latter via
pegs 30 and 31, continued rotation of the ring 4 in direction
E.sub.3 causes the armature 27 to turn inside cup 12 in opposition
to the braking action exerted by the tonguelike elements 12A, 12B,
12C and 12D, i.e. it also causes the ring 25 and its pawl 24, and
therefore the toothed disc 22 and the sleeve 15 to which this disc
is secured, and in the final resort the nut 15a, to turn by a
corresponding amount.
This movement in direction F.sub.3 of the armature 27 within cup 12
ceases as soon as the dowel 29b which is carried by the armature
abuts against the tip of stop screw 28 (FIG. 9).
As has already been described, the nut 15a of sleeve 15 is in
engagement with the threaded part 14e of shaft 14 which is
prevented from rotating by engagement of stud 9c in groove 14d so
that, upon sleeve 15 being turned, the shaft 14 is moved axially by
a distance which is dependent on the pitch of the screw thread on
the part 14e and on the angular movement of the nut 15c, and in a
direction which is dependent on the hand of the screw thread and on
the direction in which this nut is rotated.
In the illustrated mechanism, the hand of the thread on the part
14e of shaft 14 has been so chosen that, when the ring 4 is turned
in direction F.sub.3 (FIGS. 7 to 9), the shaft 14 moves in
direction F.sub.1 thereby causing the rod-cum-piston 14h to move in
the tube 7 in a manner such as to effect discharge of the liquid
contained in this tube.
By way of example, if the toothed discs 21 and 22 each comprise
fifty teeth, the nut 15a and the threaded part 14e of shaft 14 are
so dimensioned that one revolution of the nut causes the
rod-cum-piston 14h to move axially 500 .mu.m, and the diameter of
the tube portion 7a and of the rod-cum-piston 14h is 0.8 mm, then
when the toothed disc 21 or 22 is rotated by a distance equivalent
to the pitch of its teeth, the axial movement of the rod-cum-piston
14h in tube 7 is equivalent to a decrease or an increase in volume
of the space comprised between the free end of the tube and the
rod-cum-piston equal to 5 nanolitres (0.005 mm..sup.3).
Obviously, rotation of the ring 4 in a direction opposite to
F.sub.3, once this ring and the members that are kinematically
rigid therewith have come to occupy the position shown in FIG. 9,
will bring about displacement of the shaft 14 in direction F.sub.2,
i.e. movement of the rod-cum-piston 14h in the tube 7 such as to
cause liquid to by sucked into the tube.
In a manner similar to that which has been described with reference
to FIGS. 7 to 9, rotation of the ring 4 in a direction opposite to
F.sub.3 will firstly cause ring 25 to pivot about pin 26 tending to
free pawl 24 from the toothed disc 22 and to bring pawl 23 into
engagement with disc 21, the armature 27 then rotating in the cup
12 until dowel 29a abuts the tip of stop screw 28. At the end of
this rotational movement of the ring 4 in a direction opposite to
F.sub.3 the various components of the mechanism come to occupy the
position shown in FIG. 7.
IT should at this stage be pointed out that, in the illustrated
embodiment, the angular length of the free space lying between the
dowels 29a and 29b, on the one hand, and the head of the stop screw
28, on the other hand, is substantially equal to an arc equal to 10
times the pitch of the teeth on disc 21 and 22, so that the maximum
volume of liquid capable of being discharged or aspirated by the
pipette through turning the ring 4 from the FIG. 7 position to the
FIG. 9 position, or vice versa, is in fact equal to 50 nanolitres,
as stated earlier. This volume can be calibrated in a very accurate
manner by selecting a stop screw 28 having a tip of suitable
width.
As mentioned, each graduation 3a or 5a on the rings 3 and 5
corresponds to a difference in volume aspirated or discharged by
the pipette of 5 nanolitres in relation to the adjacent
graduations, all ten graduations 3a or 5a being equivalent to a
total volume of 50 nanolitres. These graduations moreover extend
over an arcuate length that is indicative of the extent to which
the armature 27 is able to rotate in the cup 12, such rotation
being limited, as described, by the dowels 29a and 29b abutting
against the tip of screw 28. It is in fact by acting on the rings 3
and 5 that it is possible exactly to set the quantity of liquid
which the illustrated pipette will discharge or aspirate in the
course of one rotary movement of armature 27, in one direction or
the other, the amplitude of such rotary movement being limited by
abutment of the screw 28 with one or other of the dowels 29a and
29b.
In the present instance, the ring 3 serves to adjust the quantity
of liquid being aspirated while the ring 5 serves to set the amount
of liquid being discharged. For these purposes the rings 3 and 5
are respectively connected by studs 36a and 37a, extending through
the slots 123 and 125 of cup 12, to annular cams 36 and 37 that are
rotatably mounted within the cup 12.
The cam 36 is placed between one radial flange of armature 27 and
the annular member 19, while cam 37 engages the other radial flange
of armature 27 and bears on a shoulder 12c provided inside the cup
12 (FIG. 1).
The profiles of cams 36 and 37 are identical: in fact these are two
similar components whose working surfaces are mounted in facing
relationship. FIG. 4 shows one such cam which consists of a ring a
of synthetic material, from the radially outer surface of which
projects a stud b, denoted previously by reference 36a, in the case
of cam 36, and 37a in the case of the other cam 37 (in FIGS. 1 and
2). The diameter d.sub.1 of the opening in ring a is slightly
greater than the external diameter of rings 18a and 18b and of the
ball and cage assembly 17. .
The ring a has over a part of its thickness a recess c of which one
portion, c.sub.1, termed the "high" portion of the cam, has a
cylindrical surface of diameter d.sub.2 corresponding very exactly
to the distance separating the pegs 30 and 31 provided on the ring
25, plus double the width of one of these pegs. The other portion,
c.sub.2, of recess c also has a cylindrical surface but the radius
of this other portion is greater than d.sub.2 /2 by an amount at
least equal to the diameter of the ports 27b and 27c in the
armature 27. The angular extent of the cam recess portion c.sub.2,
which will be termed the "hollow" of the cam, corresponds at least
to the length of the arc lying between the dowels 29a and 29b
provided on the armature 27.
The portions c.sub.1 and c.sub.2 of recess c are connected to one
another by two inclined surfaces f.sub.1 and f.sub.2, the ends of
each one of which are angularly distant from one another by a
length corresponding substantially to the angular displacement, as
viewed from the axis of shaft 14, of the pegs 30 and 31 when the
ring 25 is moved for example from one extreme position (FIG. 7) to
the other (FIG. 8).
As shown in FIGS. 1 and 3, the peg 31 carried by the ring 25
projects into the recess c of cam 36, while peg 30 projects into
the recess c of cam 37. It is to be noted, moreover, that the
"hollow" of each cam has one end which is positioned substantially
diametrically opposite the associated stub b.
It will now be explained how the cams 36 and 37 enable the amount
of liquid to be discharged or aspirated by the illustrated pipette
to be set in various ways.
To facilitate this explanation, reference will now be made to FIGS.
10 to 13 which are diagrammatic representations of the relevant
components of the mechanism, each component being shown in each
figure in a number of different operative positions identified,
where appropriate, by indicia .degree., ', " and so on,
indicium.degree. being indicative of a starting position.
In the following description, reference numerals bearing any one of
these indicia will at times identify the component as such in a
particular position and at other times simply identify a
position.
Before considering a number of possible working cases, it should
further be explained that, in FIG. 10, the straight line 27A
connecting the dowels 29a.degree. and 29b.degree. as well as the
pin 26.degree. serves only to indicate that these three components
are all rigid with the armature 27 (not shown) and that, in
operation, they move along a circular path when the armature
rotates within the cup 12 as has been described. The path followed
by the pin 26 coincides in FIG. 10 with the representation of the
ring 25.degree..
Case 1: Suction nil, discharge 50 nanolitres (total).
In this case, the position of the cams 36 and 37 is that shown in
FIG. 10. At the beginning of the discharge operation, the ring 25
is in the position 25.degree., shown by a thick continuous line,
and the armature which carries it and which is not shown, is so
positioned that the dowel 29a.degree.is in contact with the screw
28. The relative position of the cams 36 and 31 is such that the
two pegs 30.degree. and 31.degree. are each in contact with one end
part of the "high" portion of the corresponding cam.
If the stud 25a.degree. is moved in direction F.sub.3 to bring it
to position 25a' the ring 25.degree. pivots about pin 26.degree. to
occupy position 25', shown by a thin continuous line, in which pawl
24' comes into engagement with the teeth of disc 22, peg 30' having
penetrated into the hollow of the cam 37 from position 30.degree..
It will be recalled that the pivoting of ring 25 from position
25.degree. to 25' about pin 26.degree. takes place without this pin
moving, armature 27, not shown, being braked by the tonguelike
elements 12A, 12B, 12C and 12D formed in cup 12.
Subsequent movement of the stud 25a' in direction F.sub.3 causes
the armature 27 to rotate in the cup 12 until dowel 29b comes into
contact with the screw 28 at 29b' with pin 26 and dowel 29a being
moved into positions 26' and 29a'.
The ring 25 then occupies position 25" shown by a chain-dotted
line, with the stud 25a occupying position 25a" and with the pawl
24 being at 24". This pawl 24 has moved through an angle
corresponding to ten times the pitch of the teeth on toothed disc
22 which is equivalent, as described above, to a movement of the
pipette shaft 14 in direction F.sub.1 over a distance equal to a
discharge of a quantity of liquid equal to 50 nanolitres.
If the stud 25a is now moved from position 25a" to position 25a'"
in a direction opposite to F.sub.3, the ring 25 will pivot about
pin 26' in the same direction, by virtue of the fact that the
armature 27 is braked by the tonguelike elements 12A to 12A, until
the peg 31, then at 31", comes into engagement at 31'" with the
"high" portion of cam 36. By virtue of the diameter d.sub.2 that
has been chosen for this "high" portion (FIG. 47, the ring 25 is
then held by peg 31 in a central position relative to the toothed
discs 21 and 22, coinciding with that shown by the thick continuous
line, such that neither pawl 23 nor pawl 24 can come into
engagement with the associated toothed disc. Thus, in the angular
position given to the cam 36 in FIG. 10, the disc 21 can never be
driven when the stud 25a is moved in a direction opposite to
F.sub.3 : the pipette therefore aspirates nothing.
Case 2: Suction 15 nanolitres (partial), discharge 50 nanolitres
(total).
This case is illustrated by FIG. 11 for the "discharge" aspect and
by FIG. 11a for the "suction" aspect.
In relation to the case described with reference to FIG. 10, the
cam 36 has been slightly shifted in a clockwise direction (position
36.degree.) by an amount corresponding to three graduations of the
ring 3, whereas cam 37 has not moved (position 37.degree.). As can
be seen, in the starting position 25.degree. of the ring 25, the
peg 31.degree. is engaged in the "hollow" of cam 36.degree.. Upon
the stud 25a.degree. being moved in direction F.sub.3, ring
25.degree. first pivots about pin 26.degree. by virtue of the fact
that the armature 27 (not shown) is braked by the resilient
tonguelike elements 12A to 12D of the cup 12. This pivotal motion
proceeds until the pegs 30.degree. and 31.degree., which were, in
these positions, as shown in FIG. 7, bearing on a part of the edges
of the ports 27b and 27c, come to occupy positions 30' and 31'
where they bear, as shown in FIG. 8, on a part of the edges of
these ports opposite the first-mentioned part. The ring 25 is then
in position 25', indicated by a thin continuous line, and the stud
25a is in position 25a' (FIG. 11). It will be seen that, under
these conditions, the pawl 24 is in engagement with the toothed
disc 22, the peg 30 having been able to move into the "hollow" of
cam 37 to occupy position 30'. It is from then on that the disc 22
and the sleeve 15 to which it is secured come to be rotatably
driven, such rotation taking place throughout the remainder of the
movement of the ring 25 in direction F.sub.3, the pivotal pin 26 of
this ring following the curvilinear path which is imposed thereto
by the rotational movement of the armature 27 within the cup 12,
until the peg 29b comes to bear on stop screw 28.
As will be seen, this phase in the operation of the sleeve driving
mechanism comprised by the illustrated pipette is practically
identical to the discharge phase described with reference to FIG.
10.
At the end of this phase, the ring 25 occupies position 25", shown
as a chain-dotted line in FIG. 11, the toothed disc 22 having been
turned through an angle corresponding to ten times the pitch of its
teeth. This same position 25" is again to be found in FIG. 11a,
indicated by a thick continuous line.
To cause the pipette to aspirate liquid, it suffices to return the
ring 25 from position 25" to its initial position 25.degree. in
FIG. 11, i.e. position 25.sup.vi in FIG. 11a indicated as a dotted
line, by moving the stud 25a in a direction F.sub.4 opposite to
F.sub.3.
Because the armature 27 is braked by the tonguelike elements 12A,
12B, 12C and 12D, the ring 25 starts off by pivoting about its pin
26 but this pivotal motion is limited by the engagement of peg 31
with the "high" portion of cam 36 (position 31"), the ring being
then in position 25" in which neither pawl 23 nor pawl 24 engages
with its associated toothed disc 21 or 22. These discs and the
sleeve 15 are therefore not rotatably driven during much of the
movement of the stud 25a in direction F.sub.4.
But upon the peg 31 reaching position 31.sup.iv, at which time the
stud 25a occupies position 25a.sup.iv, the peg penetrates into the
"hollow" of cam 36 (position 31.sup.) and the ring 25 pivots
further anticlockwise about pivot 26.sup. to occupy position
25.sup.v indicated by a chain-dotted line. The pawl 23 then comes
into engagement with the toothed disc 21 (position 23.sup.v of this
pawl and 25a.sup.v of stud 25a).
Upon continuing to move stud 25a in direction F.sub.4, pawl
23.sup.v drives disc 21 angularly in the same direction until dowel
29a meets the stop screw 28 (the position 25.sup.vi of ring 25, as
stated earlier, coinciding with position 25.degree. in FIG. 11).
The amplitude of this movement is equivalent to an angular length
equal to three times the pitch of the teeth of disc 21 thereby
causing the shaft 14 to move in direction F.sub.2 (suction by a
distance corresponding to an increase of 3 nanolitres in the volume
of the free space in the tube 7.
Case 3: Suction 50 nanolitres (total), discharge 50 nanolitres
(total).
This is the case shown in FIG. 12 in which the two cams 36 and 37
are so positioned angularly that their "hollows" occupy
diametrically opposite positions with respect to the axis of the
toothed discs 21 and 22.
During the discharge phase (the position of the components of the
mechanism being successively identified by the indicia .degree., '
and " with the stud 25a moving in direction F.sub.3) the driving
mechanism operates in the same way as in the preceding case since
the position of cam 37 has not changed.
During the suction phase (the position of the components being
successively identified by the indicia ", '" and .degree. with the
stud 25a moving in direction F.sub.4) the mechanism operates in the
same way as during discharge, it being however understood that the
part played by the peg 31, the pawl 24 and the disc 22 during
discharge is now being played by the peg 30, the pawl 23 and the
disc 21 for suction purposes.
Case 4: Suction nil, delivery nil.
This is the case shown in FIG. 13 in which the two cams 36 and 37
are so positioned angularly that their "hollows" are in overlapping
relationship. As shown, the pawls 23 and 24 can never engage with
their associated toothed discs since the pegs 31 and 32 always move
in contact with the "high" portion of the two cams and are never
able to penetrate into their "hollows."
The driving mechanism for the sleeve 15 is placed in this position
when it is desired to fill the whole of tube 7 with liquid intended
to be distributed in several shots by the pipette, in very accurate
and particularly small quantities.
For this purpose, the sleeve 15 carries on its part 15c adjacent
the ball and cage assembly 16 a toothed wheel 40 (FIGS. 1 and 14)
that projects partially outside the cup 12 through a slot 120
formed in the latter, which wheel can be driven from outside the
pipette, for example by making use of the device shown in FIGS. 14
and 15.
This device has a frame comprising a base 41 and an upstanding
member 42 solid with this base and forming a support for the
pipette. To this end, member 42 carries two lugs 43 and 44 having
facing ends that constitute slideways between which is arranged the
pipette, by engagement in parallel grooves 121 and 122 formed on
the external surface of the cup 12 (FIG. 15). On the member 42
there is also fixed a pillarlike element 45 forming a support for a
curved and removable clamping strap serving to hold the pipette in
position when it is placed between the lugs 43 and 44.
This upstanding member 42 further carries a boss 47 on which is
rotatably mounted a toothed disc 48 to which is secured a stem 49
provided with a milled knob 50 enabling a user to rotate the disc
48 with his fingers. This disc meshes with a wheel 51 which is
kinematically connected to a toothed disc 52 through a friction
coupling, not shown, this disc 52 being so placed that it comes
into meshing engagement with the toothed wheel 40 of the pipette
when the latter is mounted on the device as shown in FIGS. 14 and
15.
The base 41 is formed at its end opposite the member 42 with a
circular recess 41a adapted to receive a container, such as the one
outlined in broken lines and referenced 53, which contains the
liquid with which the pipette is to be filled, the tube 7 of this
pipette being them dipped at its end into the container (FIG.
14).
This filling operation is effected in the following manner: once
the cams 36 and 37 have been placed as shown diagrammatically in
FIG. 13, the knob 50 is turned in direction F.sub.5 (FIG. 14)
thereby to move the shaft 14 of the pipette in direction F.sub.1
(FIG. 1).
This movement continues until the circular flange 14a of shaft 14
abuts against the shoulder 9b of the sleeve. Even if the user
carries on turning the knob 50 in direction F.sub.5 no force is
then transmitted to the pipette: because the toothed disc 52 is
locked angularly by abutment of the flange 14a on the shoulder 9b,
the kinematic connection between this disc and the wheel 51 is
interrupted by virtue of the fact that the friction coupling
interposed between these components then comes to slip.
Once the shaft 14 comes to be located in this extreme position,
after moving in direction F.sub.1, the knob 50 is turned in
direction F.sub.6 thereby causing the shaft 14 to move in direction
F.sub.2 and the rod-cum-piston 14h to aspirate into the tube 7 a
certain quantity of the liquid filling the container 53. movement
of the shaft 14 in direction F.sub.2 is interrupted by abutment of
its part 14b against the cap 11, and due to the presence of a
friction coupling between wheel 51 and disc 52. Once filled, the
illustrated pipette can be removed from the filling apparatus and
is ready for use.
In a variant, not shown, the pipette may itself have means for
driving the toothed disc 40. These means may for example consist of
an internally toothed wheel which meshes with the disc 40 and which
is rotatably mounted on the outside of cup 12.
Although the above driving mechanism has only been described with
reference to its application in a pipette, clearly such a mechanism
may have other applications, some quite different from that
described. Moreover, the driving mechanism may, according to a
variant, comprise only one toothed disc instead of two in which
case the pawls 23 and 24 of ring 25 would then cooperate with this
single disc alternately.
* * * * *