Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01L—CHEMICAL OR PHYSICAL LABORATORY APPARATUS FOR GENERAL USE
  • B01L3/00—Containers or dishes for laboratory use, e.g. laboratory glassware; Droppers
  • B01L3/02—Burettes; Pipettes
  • B01L3/021—Pipettes, i.e. with only one conduit for withdrawing and redistributing liquids
  • B01L3/0217—Pipettes, i.e. with only one conduit for withdrawing and redistributing liquids of the plunger pump type
  • B01L3/0234—Repeating pipettes, i.e. for dispensing multiple doses from a single charge

Definitions

• the present invention relates to a pipette for dispensing successive volumes of liquid by repeated action on a pusher.
• French patent application no. 2 432 161 describes a pipette comprising an oblong-shaped casing, incorporating a mechanism for adjusting the volume to be dispensed, and a syringe to be removably attached to the lower end of said casing.
• a piston capable of moving in leaktight manner inside the body of the syringe is mounted at the lower end of a push rod which can slide longitudinally through the housing.
• the drive of the push rod downwards, by action on a pusher, to dispense a predetermined volume of liquid, is carried out by means of a drive lever which can move according to a predetermined stroke between a stop. fixed lower and an adjustable upper stop.
• This lever comprises a first part traversed by a bore allowing the passage with a small clearance of the push rod and a second part extending transversely to the axis of said bore.
• the pusher is arranged to exert a pressing force in the vicinity of the free end of the second part of the lever, and to drive, by jamming effect, the push rod.
• the lever is also resiliently urged upwards, so that it automatically returns to its rest position against the upper stop when the pusher is released.
• This type of pipette has given satisfaction. However, the wear of the various component parts of the pipette results in the long run in less precision.
• the object of the present invention is to provide a new pipette having increased accuracy compared to known pipettes, even after prolonged use.
• This pipette is of the type comprising: an oblong-shaped housing, incorporating a mechanism for adjusting the volume of liquid to be dispensed, a syringe to be removably mounted at one end of the housing, comprising a syringe body provided with a passage orifice liquid and a piston rod mounted in displacement in said syringe body, - a push rod mounted in longitudinal sliding in the housing, to be connected at one end, in a removable manner, to said piston rod, a drive lever for driving the push rod and the piston rod only in the direction of said liquid passage orifice, the lever extending transversely the longitudinal axis of the push rod and being provided with a hole for the passage of the latter with little play, the lever being further mounted with the possibility of displacement in the housing, over an adjustable stroke in the longitudinal direction of the push rod, between a rest position defined by an adjustable stop of the adjustment mechanism and an end position defined by a fixed stop, and being returned to the rest position by elastic return means, said pusher
• the lever is rotatably mounted about a geometric axis perpendicularly cutting the axis of said bore substantially halfway through the latter.
• the lever is disposed on the push rod between a lower sleeve and an upper sleeve mounted to slide on the push rod, and the lever has two surfaces of revolution centered on said geometric pivot axis, arranged on either side. other of the drilling of the lever crossed by the push rod and in contact with the lower and upper sleeves.
• said surfaces of revolution are formed by balls crimped in holes in the lever.
• said pusher comprises a sheath mounted to slide inside the housing, and inside which can freely slide the push rod. It is provided at one end with a contact piece having a sharp edge intended to press the lever to cause it to tilt around said geometric axis and then move in the longitudinal direction of the push rod.
• the adjustment mechanism comprises an adjustment screw to be rotated to adjust the travel in movement of the lever and the volume distributed at each action on the pusher.
• This adjusting screw is internally traversed by the sheath and the push rod and meshes with a mechanism indicating the volume.
• the adjustment screw has an end edge defining said variable stop, and the upper sleeve has an own end edge to come into punctual contact therewith.
• the operating button equipping the pusher comprises a first part mounted to slide on a second part, with the interposition of a first return spring.
• a second return spring with a lower stiffness constant than the first is interposed elastically between the housing and said second part to resiliently return the pusher away from said liquid passage orifice.
• the stiffness constant of said elastic return means urging the lever towards its rest position is less than the stiffness constant of the first and second return springs.
• the syringe and the plunger rod are removably attached to the pipette housing by means of a clamp which is in the form of a part, the upper part of which is secured to the lower end of the push rod, the middle part of which has a recess suitable for receiving the free upper end of the piston rod, and the lower part of which comprises elastic branches allowing the introduction and maintenance of the piston rod, and the lower end of the housing comprises means capable of removably fixing the body of the syringe while allowing the free sliding of the clamp and the piston rod.
• the middle part of the clamp has a recess defined by the free upper faces of the clamps, by a shoulder surface, by a transverse surface and by a longitudinal surface.
• FIGS. 1 and the are views in longitudinal section of two different embodiments of a pipette according to the invention
• FIG. 2 is a partial longitudinal section, on an enlarged scale, of the pipette shown in FIG. 1
• FIG. 3 represents, in perspective, the drive lever traversed by the push rod
• FIGS. 4 to 7 represent successive positions of the drive lever during the use of the pipette
• - FIGS. 8 to 10 represent successive positions of the operating button equipping the pusher of the pipette during the use thereof
• FIG. 11 is a perspective view of a pliers for fixing the piston tail
• - FIGS. 12 and 1 3 illustrate the positioning by pivoting of the plunger syringe assembly.
• the pipette according to the invention shown in FIG. 1 comprises a housing 1 made of plastic, of oblong shape, suitable for gripping by a user.
• a syringe 2 is mounted so removable at the lower longitudinal end of the housing 1 for withdrawing and distributing successive volumes of liquid.
• This syringe 2 has a generally cylindrical body 3 of revolution about an axis X, extended below by a frustoconical tip 4 open at its top in 4 'for the passage of the liquid.
• a plastic piston rod 5 is slidably mounted in the body 3, the seal being ensured by an annular lip 6 located in the lower part of the piston rod 5.
• the latter has, below the lip 6, a conical lower end 7, shaped to engage in the frusto-conical end piece 4 in order to expel the liquid contained therein as best as possible when the piston rod 5 reaches the end of its travel downwards.
• the body 3 has at its upper end 8 a rim projecting outwards and retained by blistering in an annular groove 9 of the housing 1, or by any other equivalent arrangement which allows easy assembly and disassembly of the syringe assembly and piston on the open lower end of the housing 1.
• the annular groove 9 is formed on the radially internal surface of a housing 10 generally cylindrical of revolution around the axis X, formed in the lower part of the housing 1, and in which the piston rod 5 of the syringe 2 can be raised when '' a liquid sample is taken.
• the wall 11 of the housing 1 delimiting this housing 10 is generally cylindrical of revolution around the axis X, and it is open over a part of its length, parallel to the axis X, to form a longitudinal slot 12 intended for the passage d 'A drive finger 13 of the piston rod 5, as will be explained below.
• the piston rod 5 has at its upper end a coupling part 14 detachably connected to the lower end of a push rod 15 mounted for longitudinal sliding along the axis X in the housing 1.
• the rod thrust 15 is cylindrical of revolution around the axis X for its upper part slidably mounted in the housing 1 and widens at its lower end to form a housing 16 cylindrical of revolution around the axis X, intended to receive the coupling part 14 of the piston rod 5.
• This coupling part 14 is corrugated, having a succession of three friction discs 17, of the same diameter, regularly spaced along a core 18 of smaller diameter than the discs 17. The retention of the coupling part 14 inside the housing 16 is effected by friction.
• the drive finger 13 is fixed to the wall 19 of the push rod 15 delimiting the housing 16, and extends through the slot 12.
• the drive finger 13a has been raised to the upper part of the housing 1 to facilitate access to the drive finger 13a for a user handling the pipette with only one hand.
• the finger 13a extends internally to the housing by a sort of strip 13 b joining it with a control and fixing part of the piston tail.
• the lower part of this strip 13 b. ending in a brightly colored tongue which becomes visible from the outside of the housing, at the end of the pipette stroke, that is to say when the body of the syringe 2 is about to empty completely.
• the housing 1 houses in the upper part a mechanism 20 for adjusting the volume to be dispensed which will be described in more detail below, as well as an indicator assembly 21 for this volume, coupled to the adjustment mechanism 20.
• the sheath 40 descends and drives, by means of a unidirectional transmission 24, the push rod 15 and the piston rod 5 downwards, this that is to say in the direction of the orifice 4 ′ for the passage of the liquid, in order to distribute the liquid, while the return movement upwards of the sheath 40 takes place alone under the action of elastic return means constituted by a helical spring 25, independently of the push rod 15 and the piston rod 5 which each retain their position in the housing 1 and the body 3 of the syringe 2, under the effect of the friction exerted by the lip 6 on the body 3 of the syringe 2.
• the elastic return means are produced in the form of a helical spring 25 a which no longer works in compression like the spring 25, but in tension.
• the unidirectional transmission 24 which is now described more particularly with reference to FIG. 2 comprises a lever 26 generally extending transversely to the axis X, having a central circular bore 27 for the passage with a small clearance of the push rod 15 This small clearance allows angular movement of the lever 26 between a rest position where the axis of the central bore 27 is substantially parallel to the axis X (which allows free movement of the lever 26 on the push rod 15) and an oblique downward position relative to the X axis (for driving the push rod 15 by wedging effect).
• the drive lever 26 is disposed on the push rod 15 between an upper sleeve 28 and a lower sleeve 29, both slidably mounted on the latter.
• a helical spring 30 working in compression is placed between the lower sleeve 29 and a ring 31 serving as a fixed stop, axially retained against an internal shoulder 32 of the housing 1.
• the ring 31 closes the housing 10 on its underside, and has the side opposite to the latter a central part 33 cylindrical of revolution around the axis X, bored for the passage of the push rod 15 and a wall 34, cylindrical of revolution around the axis X, providing with the central part 33 a annular groove 35 open upwards.
• the wall 34 is in contact by its radially external surface with the housing 1.
• the helical spring 30 comes to bear axially, at its lower end 36, in the bottom of the annular groove 35, and at its upper end 37 against a shoulder 38 of the lower sleeve 29.
• the sheath 40 of the pusher 22 is cylindrical of revolution around of the axis X, and the push rod 15, metallic, can slide freely inside the latter.
• the sheath 40 is extended, at its lower end, by a contact piece 41 intended to come to press on the lever 26 to cause it to tilt and then, after jamming of the push rod 15, in displacement along the axis X in same time as the push rod 15.
• the contact piece 41 has a first part 44 connecting at one end to the sheath 40, - extending radially outwards 8
• the upper sleeve 28 is generally cylindrical of revolution around the X axis; it is bored from its upper end edge 39 over more than half of its length to receive the lower end of the sleeve 40.
• the wall 42 of the upper sleeve 28 delimiting the bore intended to receive the sleeve 40 is open on its periphery to form a longitudinal slot 43 intended for the passage of the contact piece 41.
• the assembly constituted by the lever 26 and the lower 29 and upper 28 sleeves moves inside a guide piece 49 generally tubular around the axis X, open downwards and closed at its upper part, except a thread 63 centered on the X axis for the passage of a hollow adjustment screw 62, inside which the sleeve 40 and the push rod 15 can slide.
• the guide piece 49 has a lower end 50 shouldered , engaging in the annular groove 35 of the ring 31, in contact with the radially internal surface of the wall 34, until the shoulder abuts against the upper edge of the wall 34.
• the guide piece 49 comes in support, by its upper end edge 51, against the volume indicator assembly 21.
• the lever 26 is shown with the push rod 15 in perspective in FIG. 3. It is mainly constituted by a plate extending perpendicular to the axis of the central bore 27, having a first part 53 crossed in its center by the central bore 27 for the passage with a small clearance of the push rod 15 and a second part 54 laterally extending the first part 53 to serve as a support for the contact piece 41.
• the first part 53 is crossed by two holes 55 and 56 located on either side of the central hole 27, each serving as a housing for a ball 57 or 58 retained by crimping in the wafer.
• the plane P 2 containing the axes of the central bore 27 and those of the holes 55 and 56 receiving the balls 57 and 58 extends perpendicularly to a median plane Pi for the lever 26, containing the axis of the central bore 27 and the direction along which extends the second part 54 of the lever 26.
• the second part 54 has, in section in a plane parallel to the plane? 2 a rectangular section.
• the balls 57 and 58 are interposed axially between the lower sleeve 29 and the upper sleeve 28, and constitute guide means for guiding the tilting of the lever 26 when the contact piece 41 extending below the sheath 40 presses on the end 48 of the second part 54.
• This tilting takes place around a geometric axis of rotation Y perpendicularly intersecting the axis X, substantially halfway through the central bore 27.
• a more or less pronounced clearance, caused by wear, for the passage of the push rod 15 in the central bore 27 of the lever 26 results in accordance with the invention by a more or less large tilting of the lever 26 around the geometric axis of rotation Y, until the wedging of the push rod 15 against the edges of the central bore 27.
• the geometric axis of rotation Y of the lever 26 remains fixed during the tilting operation of the latter.
• the upper sleeve 28 has, on its upper end edge 39, an upwardly convex boss 60, the apex of which defines point contact with the lower end edge 61 of the adjusting screw 62.
• the latter is traversed internally by the sleeve 40 as indicated above and it is externally threaded to engage, at the bottom, with the internal thread 63 of the guide piece 49.
• the assembly formed by the adjusting screw 62 and the guide piece 49 constitutes the aforementioned mechanism 20 for adjusting the volume to be dispensed, making it possible to vary the lowering stroke of the lever 26, therefore that of the push rod 15 and of the piston rod 5, at each action on the pusher 22, as will be specified below.
• the adjusting screw 62 has at its upper end a flange 64 accessible from the outside of the housing 1 by the user, through openings not shown formed in the housing 1.
• the flange 64 is advantageously knurled on its radially external surface to facilitate manual rotation of the adjusting screw 62 by the user.
• a brake can also be added to the adjusting screw 62, to exert a friction force with the housing 1 and prevent inadvertent adjustment, during use, of the volume selected by the user.
• the flange 64 of the adjustment screw 62 rotates inside a part 65 generally cylindrical of revolution around the axis X, provided with openings intended to coincide with those of the housing 1 for access, from the outside, to the collar 64.
• a closing washer 66 is attached to the upper end edge of the part 65. The latter is drilled at its lower part to receive a nut 67 through which the adjusting screw 62 passes.
• the indicator assembly 21 is known in itself and will not be described in detail. It is, in the example shown, of the type comprising three drums indicating the volume to be dispensed, juxtaposed and meshing with each other and with the adjusting screw 62, in a manner known per se. The volume to be dispensed is indicated to the user by the drums through a transparent window 68.
• FIG. 5 shows the sheath 40 of the pusher 22 at the end of a first stroke, called the comfort stroke, by a distance B from the rest position of the sheath 40 until the edge 47 contacts the lever 26.
• the sleeve 40 drives, through the contact piece 41, the lever 26 downwards, and the movement of the latter is accompanied by the movement of the push rod 15, due to the jamming of the latter in the central bore 27.
• the downward movement of the lever 26 is transmitted to the lower sleeve 29 by the balls 57 and 58, and the latter is moves down against the coil spring 30, until the lower end edge 70 of the lower sleeve 29 stops against the upper end edge 71, flat and generally perpendicular to the axis X, of the central section 33 of the ring 31.
• the push rod 15 is lowered by a distance A corresponding to the initial distance between the lower end edge 70 of the lower sleeve 29 and the upper end edge 71 of the central part 33 of the ring 31.
• the push rod 15 drives the piston rod 5 downward and a predetermined volume of liquid is expelled through the orifice 4 '.
• the lever 26 rises alone, independently of the push rod 15, due to the absence of jamming of the latter in the bore 27 when the contact piece 41 n does not exert pressure on the end 48.
• the lever 26 is returned by the helical spring 30 to its rest position corresponding to the abutment of the upper sleeve 28 against the lower end edge 61 of the adjusting screw 62 .
• the user can modify the initial difference between the lower end edge 70 of the lower sleeve 29 and the upper end edge 71 of the central part 33 of the ring 31, therefore the distance A and the volume which will be dispensed during the next pressure exerted on the operating button 23.
• the operating button 23 comprises two parts assembled telescopically one on the other. More specifically, the operating button 23 has a lower part 81 bored at 82 to be fitted on - the upper end edge of the sheath 40, until it stops in the bottom of the bore 82. The latter is bordered on the outside, downwards, by a cylindrical wall 83 forming with the sheath 40 an annular groove 84 open downwards to receive the upper end of the spring 25. The latter works in compression and is resiliently interposed between the bottom of the groove 84 and the closing washer 66, crossed in its center by the sheath 40.
• the operating button 23 also has a part upper 80, which is slidably mounted along the X axis on the lower part 81.
• the latter is provided at its upper end with retaining tabs 86 each having, on the radially external side, a tooth forming a projection, suitable for coming into abutment against a shoulder 87 formed on the radially internal surface of the upper part 80, to axially retain the latter.
• a helical spring 88 working in compression is mounted inside the upper part 80 to elastically interpose between the upper front face 89 of the lower part 81 and the bottom 90 of the upper part 80, and to elastically urge the latter towards the top until the teeth of the tongues 86 stop against the shoulder 87.
• the syringe 2 Before using the pipette, the syringe 2 is filled with a liquid to be dispensed, by immersing the frustoconical tip 4 in the liquid to be withdrawn and then manually raising the piston rod using the drive finger 13 5 in the housing 10.
• the push rod 15 rises freely inside the sheath 40 of the pusher 22, the lever 26 being in its rest position.
• the user presses the upper part 80 of the operating button 23.
• the pushing force is transmitted by means of the spring 88 at the lower part 81, therefore at the sleeve 40, and the latter moves downwards until the lower sleeve 29 stops against the ring 31.
• the return spring 25 for the sleeve 40 in its position rest is then compressed. If the user continues to press the operating button 23, the upper part 80 covers the lower part 81 as shown in FIG. 10. In fact, the user does not feel that the spring 88 is compressed until after the sleeve lower 29 has reached the ring 31. It is thus ensured that the user drives the operating button 23 a sufficient distance so that the push rod 15 is driven over the entire stroke A downwards.
• the lower sleeve 29 remains in abutment for the time of the relaxation of the spring 88. The jolts on the push rod 15 are thus limited and delivery is ensured in its entire volume of liquid to be dispensed.
• the stiffness constant of spring 88 is greater than that of springs 25 and 30.
• the stiffness constant of spring 25 is greater than that of spring 30.
• Figure 1 1 shows, in perspective, a particularly advantageous embodiment of the means of fixing the syringe 3 and piston rod 5 assembly to the lower end of the pipette housing 1.
• a clamp 100 which has been specially designed to allow placement and rapid replacement of the lower part of the pipette.
• the clamp 100 is constituted by a mass piece placed at the lower end of the case 1 of the pipette in the position illustrated by the sections of Figures la and Figures 12 and 13.
• these elastic branches 101 are located at the lower part of the clamp 100 which in its middle part has a recess intended to allow the mounting and dismounting of the piston tail.
• This recess is delimited by three generally flat surfaces which are essential for the mounting and the retention of the piston tail previously described more in details.
• a shoulder surface 103 which is constituted by a small flat surface extending in the longitudinal axis of the pipette and serving as a surface for hooking and supporting the upper disc. friction 17 of the tail of the piston rod 5.
• the hooking function of the shoulder surface 103 is illustrated by the position of the syringe piston assembly of FIG. 12.
• the clamp 100 has a transverse surface 104 which is not strictly perpendicular to the axis X of the pipette but has a slight inclination of a few degrees thus creating a clearance allowing the pivoting of the upper disc 17 of the rod of piston 5. It is therefore not strictly speaking a stop or support surface.
• the middle position of the clamp 100 includes a longitudinal surface 105 of transverse support of the tail of the piston rod. It can be seen in FIG. 13 that after tilting of the plunger syringe assembly the different friction discs 17 come into contact with this surface 105 along one of their generatrices.
• the pipette further comprises a metal clamp 106 of suitable elasticity blocking the lower part of the pipette in its correct working position, as illustrated in FIG. 13.
• This clamp 106 has the essential function of keep the syringe 2 in contact with the lower retaining flange 107 of the pipette case, while the piston rod 5 can move with the clamp 100 inside the housing 10 of the pipette.
• the upper part 108 of the clamp 100 comprises means for securing with the upper end of the push rod 15 to control the longitudinal movements of the clamp 100 and piston 5 assembly in said housing 10 of the pipette.

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• Health & Medical Sciences (AREA)
• Clinical Laboratory Science (AREA)
• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Devices For Use In Laboratory Experiments (AREA)
• Infusion, Injection, And Reservoir Apparatuses (AREA)

Applications Claiming Priority (3)

Publications (2)

Family

ID=9466320

Family Applications (1)

Country Status (8)

Cited By (6)

Families Citing this family (34)

Family Cites Families (11)

• 1994
  • 1994-08-16 FR FR9410035A patent/FR2723700B1/fr not_active Expired - Fee Related
• 1995
  • 1995-08-16 WO PCT/FR1995/001084 patent/WO1996004991A1/fr not_active Ceased
  • 1995-08-16 CN CN95195245A patent/CN1158579A/zh active Pending
  • 1995-08-16 FI FI970642A patent/FI970642L/fi not_active Application Discontinuation
  • 1995-08-16 US US08/793,161 patent/US5770159A/en not_active Expired - Lifetime
  • 1995-08-16 EP EP95927786A patent/EP0776247B1/de not_active Expired - Lifetime
  • 1995-08-16 JP JP50707896A patent/JP3772348B2/ja not_active Expired - Lifetime
  • 1995-08-16 DE DE69505827T patent/DE69505827T2/de not_active Expired - Lifetime

Non-Patent Citations (1)

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