US3615240A

US3615240A - Micropipette comprising a pawl mechanism for driving a rotary member

Info

Publication number: US3615240A
Application number: US13779A
Authority: US
Inventors: Manuel Claude Sanz
Original assignee: Micromedic Systems Inc
Current assignee: ICN Micromedic Systems Inc
Priority date: 1969-02-26
Filing date: 1970-02-24
Publication date: 1971-10-26
Anticipated expiration: 1988-10-26
Also published as: DE2009889A1; IL33974A0; CH508202A; GB1301342A; NL7002691A; SE359627B; IL33974A; FR2032416A7

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.

Description

0 United States Patent 1 13,615,240

[72] Inventor Manuel Claude Sam [56] R f en e Cit d Canton, Geneva, Switzerland UNITED STATES PATENTS 9 $3 1970 2,988,321 6/1961 Gilmont 23/292 x {i f Z 1971 3,248,950 5/1966 Pursell et a1. 222/309 x S t 1 3,292,667 12/1966 Bittner et al. 23/253 X [73] Assgnee g m fi i g 3,302,462 2/1967 PUl'Sell 73/4234 P 3 Priority Feb. 26,1969 3,421,858 1/1969 Qu1nn 23/253 [33] Switz rland Primary Examiner-Morris O. Wolk [31] 2864/69 Assistant Examiner-R. E. Serwin Artorneys-G. W F. Simmons, A. R. Eglington and Gerry J.

Elman ABSTRACT: A device for drawing and distribution of liquid, as exemplified in a pipette, operated alternately in two [541 MICROPIPETTE COMPRISING A PAWL jgjjfij'gfjgfg 'fif and-d'strbutmg h-aYmg qu1 stormg purposes, comprising a pawl MECBANISM DRIYING A ROTARY MEMBER mechanism for driving a rotary member, an armature 25 Clams Drawmg Figs rotatably mounted around the rotary member, a support on [52] US. Cl 23/259, the armature for pivotal movement at right angles to the rota- 23/253 R, 23/292, 73/4254 P, 73/4256, 222/282, tional axis of the armature, first and second pawls secured to 222/309 opposite sides of the support axis, and capable of being selec- [51] l1nt.Cl1 G01n 1/00, tively brought into engagement with the teeth of the rotary GOln 1/14 member by rocking the support in one direction in the case of [50] Field of Search 23/253, the first pawl, and in the opposite direction in the case of the second pawl.

PATENTEUncr 26 I9?! SHEET 1 (1F 7 INVENTOR MANUEL CLAUDE SANZ ATTORNEYS PATENTEDum 26 1971 3,615,240

SHEET 2 CF 7 INVENTOR MANUEL CLAUDE SANZ ATTOR NEYS PATENTED B 26 3,615,240

SHEET 3 OF 7 AINVENTOR MANUEL CLAUDE SANZ wah ATTORNEYS PATENTEDum 26 I971 SHEH b [1F 7 INVENTOR MANUEL CLAUDE SANZ TTORNEYS 3,6l.5,2dO

PATENTEUHET 2s ISYI SHEET 5 BF 7 INVENTOR MANUEL CLAUDE SANZ ATTORNEYS PMENTEUUET 2s IQYI 3, 1 5 240 SHEET 70F 7 INVENTOR F G [5 MANUEL CLAUDE SANZ ATTORNEYS MICROPIPETTE COMPRISING A PAWIL MECHANISM FOR DRIVING A ROTARY MEMBER 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. 11 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. la 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. I pipette, taken along the line III-III of FIG. 2;

FIG. 4 is a perspective view of a component of the FIG. ll pipette;

FIG. 5 is a side view showing part of the casing for the FIG. I pipette;

FIG. 6 is a diagrammatic cross section of the pipette along the line VlVl of FIG. 5;

FIGS. 7 to 9 ARE CROSS SECTIONS OF THE PIPE'I'IE 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. 1% and 15 represent respectively a front elevational view and a plan view of the FIG. ll pipette mounted on a sup port device sewing to fill the pipette. The illustrated pipette comprises a'tubular handle l at the :top end of which is arranged a head 2 carrying firstly, three rotary rings 3, d 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 d, 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 of plastics material and which is closed off at one end by a cap llll 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 114 having an annular flange Ma 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 141 in direction F by abutment against a shoulder 9b of the sleeve, the amplitude of possible displacement of the shaft in direction F opposite to F opposite to F 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 Me 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 Mb comes into contact with the cap Ill, or vice versa; this cylindrical portion is formed with a longitudinal groove 14d within which is freely engaged the tip of a stud 90 which projects into the bore of sleeve 9 and prevents any rotary displacement of shaft 14 during axial sliding movement thereof.

This cylindrical portion Mic of the shaft is extended by a threaded part Me with which engages a nut a 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 142, during axial movement of the shaft.

The shaft 14 terminates in a cylindrical element 143 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 Mix. The diameter of rod 14h is so sized as to slide with a fairly close fit in'the tube portion 7a when the shaft M, 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 and the liquid filling the tube to be discharged therefrom, upon movement of the shaft in the opposite direction F 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 113a. At one end of ring 6b is formed a cylindrical aperture portion in which is engaged a sleeve of synthetic material 60, passing through the nut 6a via a passage 60 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 be 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 60 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 or F, 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 as will now be described.

The sleeve 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 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 270, 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 deter mines 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 suflicient to enable ring 25 to pivot about pin 26 to the extent indicated above, without rod 250 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 813 (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 88 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 88 by engagement of an internal portion 40 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 88 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 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 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 41. This quantity depends on the axial distance travelled by the rod 16h of shaft 16 within the portion 7a of tube 7, such distance being directly related to the angular displacement of the nut a, i.e. of the sleeve 15 carrying the

toothed discs

21 and 22. The drive of armature 27 and of

ring carrying pawls

23 and 22, by means of which

discs

21 and 22 are rotated, is dependent on the ring 4, FIGS. 7 and 2 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 2 shifted angularly through 90 in an anticlockwise direction, the ring 6 has been moved to an extreme left position such that the dowel 29a of armature 27 contacts the tip of stop screw 22, 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 241 is disengaged from disc 22.

When ring 6 is turned in direction F (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 tonguelilte 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 270 which are formed in armature 27 and in which are engaged pegs 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 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 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 2d, 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 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 22 (F IG. 9).

As has already been described, the nut 15a of sleeve 15 is in engagement with the threaded part Me of shaft 141 which is prevented from rotating by engagement of stud 9c in groove 14d so that, upon sleeve 15 being turned, the shaft 16 is moved axially by a distance which is dependent on the pitch of the screw thread on the part Me 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 142 of shaft 14 has been so chosen that, when the ring 4 is turned in direction F (FIGS. 7 to 9), the shaft 14 moves in direction F 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 Me of shaft 14 are so dimensioned that one revolution of the nut causes the rod-cum-piston 14h to move axially 500 ,um, and the diameter of the tube portion 7a and of the rod-cum-piston 1611 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 16h 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 nanolitrcs (0.005 mm).

Obviously, rotation of the ring 6 in a direction opposite to F once this ring and the members that are lrinematically rigid therewith have come to occupy the position shown in MG. 9, will bring about displacement of the shaft 141 in direction F i.e. movement of the rod-cum-piston 14th 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 will firstly cause ring 25 to pivot about pin 26 tending to free pawl 26 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 23. At the end of this rotational movement of the ring 41 in a direction opposite to F 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 2%, on the one hand, and the head of the stop screw 26, 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 6 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 29 having a tip of suitable width.

As mentioned, each graduation 3a or 50 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 22 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 earns 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. il 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 360, in the case of

cam

36, and 37a in the case of the other cam 37 (in FIGS. 1 and 2). The diameter d, of the opening in ring a is slightly greater than the external diameter of rings 12a and Nb 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 termed the high" portion of the cam, has a cylindrical surface of diameter d 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, 0 of recess c also has a cylindrical surface but the radius of this other portion is greater than d,/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 which will be termed the hollow" of the cam, corresponds at least to the length of the are lying between the

dowels

29a and 29b provided on the armature 27.

The portions and c, of recess c are connected to one another by two inclined surfaces f, and f,, 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 0 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 and so on, indicium 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 and 29bas well as the pin 26 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. I 0 with the representation of the ring 25 Case 1: Suction nil, discharge 50 nanolitres (total).

In this case, the position of the earns 36 and 37 is that shown in FIG. 10. At the beginning of the discharge operation, the ring 25 is in the position 25, shown by a thick continuous line, and the armature which carries it and which is not shown, is so positioned that the dowel 29ais in contact with the screw 28. The relative position of the

cams

36 and 31 is such that the two

pegs

30 and 31 are each in contact with one end part of the high" portion of the corresponding cam.

If the stud 25a is moved in direction F to bring it to position 25a the ring 25 pivots about pin 26 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. It will be recalled that the pivoting of ring 25 from position 25 to 25' about pin 26 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 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 290 being moved into positions 26' and 29a.

The ring 25 then occupies position 25" shown by a chaindotted 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 1 over a distance equal to a discharge of a quantity of liquid equal to 50 nanolitres. I

If the stud 25a is now moved from position 25a to position 251' in a direction opposite to F 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 a, 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,: the pipette therefore aspirates nothing.

Case 2: Suction l5 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) by an amount corresponding to three graduations of the ring 3, whereas cam 37 has not moved (position 37). As can be seen, in the starting position 25 of the ring 25, the peg 31 is engaged in the hollow" of cam 36. Upon the stud 25a being moved in direction F ring 25 first pivots about pin 26 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 and 31, 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 250 (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= 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 in FIG. 11, i.e. position 25" in FIG. 11a indicated as a dotted line, by moving the stud 25a in a direction F opposite to F 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 But upon the peg 31 reaching position 31", at which time the stud 25a occupies position 25a, the peg penetrates into the hollow" of cam 36 (position 31) and the ring 25 pivots further anticlockwise about pivot 26 to occupy position 25 indicated by a chain-dotted line. The pawl 23 then comes into engagement with the toothed disc 21 (position 23" of this pawl and 25a of stud 25a).

Upon continuing to move stud 25a in direction F pawl 23' drives disc 21 angularly in the same direction until dowel 29a meets the stop screw 28 (the position 25 of ring 25, as stated earlier, coinciding with position 25 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, (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 5O 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 and with the stud 25a moving in direction F 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 with the stud 25a moving in direction F,) the mechanism operates in the same way as during discharge, it being however understood that the part played by the peg 31, the pawl 21 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.

Thisis the case shown in FIG. 13 in which the two earns 36 and 37 are so positioned angularly that their hollows are in overlapping relationship. As shown, the

pawls

23 and 21 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 10 (FIGS. 1 and 11) that projects partially outside the cup 12 through a slot 121) formed in the latter, which wheel can be driven from outside the pipette, for example by making use of the device shown in FIGS. 11 and 15.

This device has a frame comprising a base 11 and an upstanding member 12 solid with this base and forming a support for the pipette. To this end, member 12 carries two

lugs

13 and 11 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 12 there is also fixed a pillarlike element 15 forming a support for a curved and removable clamping strap serving to hold the pipette in position when it is placed between the

lugs

13 and 11.

This upstanding member 12 further carries a boss 17 on which is rotatably mounted a toothed disc 11 to which is secured a stem 19 provided with a milled knob 50 enabling a user to rotate the disc 18 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 10 of the pipette when the latter is mounted on the device as shown in FIGS. 11 and 15.

The base 11 is formed at its end opposite the member 12 with a circular recess 11a 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. 11).

This filling operation is effected in the following manner: once the earns 36 and 37 have been placed as shown diagrammatically in FIG. 13, the knob 51 is turned in direction F (F16. 11) thereby to move the shaft 11 of the pipette in direction 1F, (FIG. 1).

This movement continues until the circular flange 11a of shaft 11 abuts against the shoulder 9b of the sleeve. Even if the user carries on turning the knob 51 in direction F no force is then transmitted to the pipette: because the toothed disc 52 is locked angularly by abutment of the flange 110 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 11 comes to be located in this extreme position, after moving in direction F the knob 50 is turned in direction I" thereby causing the shaft 11 to move in direction F and the rod-cum-piston 11h to aspirate into the tube 7 a certain quantity of the liquid filling the container 53. movement of the shaft 11 in direction F is interrupted by abutment of its part 11!; 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 11. These means may for example consist of an internally toothed wheel which meshes with the disc 11) 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 21 of ring 25 would then cooperate with this single disc alternately.

Iclaim:

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.

1. 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 are 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 earns, 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 predeterrnining 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

1. 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.

Claims

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.