EP0006556A1 - Method and device for depositing a predetermined quantity of a liquid substance in a receptacle - Google Patents

Abstract

The invention relates to a method and a device for depositing in a container a predetermined dose of a liquid substance. The device comprises a pipette (1) provided with a piston (5) for withdrawing a quantity of substance, a sleeve (19) for cooling the lower tube (2) of the pipette and means (23, 24, 25) for cut the cord (40) of frozen substance leaving the calibrated tube when pressure is applied to the piston. Application to the dosing of reagents in laboratory analyzes.

Description

The present invention relates to a method and a device for depositing in a container a predetermined dose of a liquid substance.

It is known that in order to carry out a laboratory analysis it is often necessary to have a predetermined dose of a liquid substance such as a reagent in a small container. For this, a graduated pipette is commonly used with the aid of which a certain quantity of reagent is withdrawn by suction and part of this sample is allowed to flow by gravity into the container, the volume of the dose of reagent thus deposited being determined by the level difference read on the graduation of the pipette.

But when the dose of reagent is very low this method has the disadvantage of being imprecise.

Indeed, as a result of capillarity phenomena in the calibrated tube, the dose deposited in the container can only be determined with an accuracy corresponding to the volume of a drop, this volume not being negligible compared to that of the dose.

In addition, the method mentioned above is long, relatively delicate and unsuitable for use in an automatic chain. It is therefore impractical when you have a large number of doses to prepare.

The object of the present invention is to overcome these drawbacks and to implement a precise method for depositing a very low dose of a liquid substance in a container, this method being able to be easily applied to an automatic filling device.

• - à refroidir une partie inférieure de la pièce tubulaire, cette partie inférieure étant un tube calibré,
• - à appliquer une pression verticale dirigée vers le bas sur le niveau supérieur de la substance prélevée dans la pièce tubulaire, le refroidissement étant suffisamment intense pour que, sous l'influence de ladite pression, un cordon continu vertical de substance gelée se forme sous le tube calibré,
• - et à couper le cordon de manière qu'un fragment de longueur prédéterminée détaché du cordon soit reçu par gravité dans le récipient, ce fragment constituant après liquéfaction ladite dose prédéterminée.

The subject of the present invention is a method for depositing a predetermined dose of a liquid substance in a container, first consisting in taking a sample of this substance in a tubular piece arranged vertically above the container, characterized in that it then consists,

• to cool a lower part of the tubular part, this lower part being a calibrated tube,
• - to apply a vertical pressure directed downwards on the upper level of the substance taken from the tubular part, the cooling being intense enough so that, under the influence of said pressure, a continuous vertical bead of frozen substance is formed under the calibrated tube,
• - And to cut the cord so that a fragment of predetermined length detached from the cord is received by gravity in the container, this fragment constituting after liquefying said predetermined dose.

• - des moyens de refroidissement du tube calibré,
• - des moyens pour appliquer une pression verticale dirigée vers le bas sur le niveau supérieur de la substance prélevée, ces moyens agissant simultanément avec lesdits moyens de refroidissement pour former sous le tube calibré un cordon continu vertical de substance gelée
• - et 'des moyens pour couper le cordon de manière à détacher un fragment de longueur prédéterminée du cordon, ce fragment reçu par gravité dans le récipient constituant après liquéfaction ladite dose prédéterminée.

The present invention also relates to a device for depositing in a container a predetermined dose of a liquid substance, comprising a tubular piece arranged vertically above the container and means for taking a sample of this substance from the tubular piece, characterized in that the lower part of the tubular part is constituted by a calibrated tube and that it further comprises

• - means for cooling the calibrated tube,
• - Means for applying a vertical pressure directed downwards on the upper level of the sampled substance, these means acting simultaneously with said cooling means to form under the calibrated tube a continuous vertical bead of frozen substance
• - And 'means for cutting the cord so as to detach a fragment of predetermined length of the cord, this fragment received by gravity in the container constituting after liquefaction said predetermined dose.

Several particular embodiments of the object of the present invention are described below, by way of example, with reference to the accompanying drawings, in which FIG. 1 schematically represents an embodiment of the device according to the invention and Figure 2 is a partial sectional view, more large scale, of a device member illustrated in FIG. 1.

In FIG. 1 is shown a tubular part 1, for example made of glass, essentially composed of a calibrated tube 2, of internal section of one square millimeter for example, surmounted by a filling tube 3 of larger diameter. The two tubes are aligned along the same vertical axis and their interior volumes are in communication by a cylindrical connection wall 4. A piston 5 is placed inside the tube 3. One end of a vertical rod 6 is fixed on the piston 5 while its other end engages in an eyelet 7 located at one end of an arm of a lever 8 rotatably mounted about a horizontal axis 9. The arm of the lever 8 opposite to that which comprises the eyelet 7 is in contact with a cam 10 rotatably mounted about a horizontal axis 11. Contact between the lever 8 and the cam 10 is provided by a spring 12, one end of which is secured to a point 13 fixed in the plane vertical rotation of the lever 8, the other end of this spring being fixed to the lever 8.

The cam 10 is rotated about the axis 11 by an electric motor 14 via a reduction gear 39.

A lateral opening 15 located at the lower part of the tube 3 is connected by a pipe 16 to a reservoir 17 containing a liquid substance 18 such as a reagent. A valve 38 is placed inside the pipe 16.

Around the calibrated tube 2 is placed an enclosure 19 connected by two pipes 20 and 21 to a refrigeration unit 22.

Below the tubular part 1, is arranged a laser generator 23, for example of the neodymium doped glass type, emitting a horizontal laser beam 24 on the path of which is placed an optical system such as a converging lens 25 capable of focusing the energy of the beam 24 at a point 26 located on the extension of the vertical axis 27 of the calibrated tube 2.

A light emitting diode 28 powered by a circuit 29 emits a horizontal light beam 30 which intersects the axis 27 at a point 31 located below point 26 at a predetermined distance 32 which can be of the order of 5 millimeters. The beam 30 is intercepted beyond point 31 by a photoelectric receiver 33 whose electrical output is connected to a trigger circuit 34, itself connected to the laser generator 23.

Below point 31, an electric furnace 35 of tubular shape is arranged vertically so as to surround the axis 27.

A container 36 is placed below the oven 35, substantially along the axis 27.

Figure 2 is a partial sectional view of the tubular part 1 showing on a larger scale the calibrated tube 2. It is visible in this figure that the inner cylindrical surface of the tube 2 is coated with a layer 37 of a material to low coefficient of friction such as polytetrafluoroethylene, this layer being able to extend as shown towards the connection wall 4.

The device described above and illustrated by Figures 1 and 2 operates in the following manner.

The rotation of the cam 10 causes an alternating rotation from bottom to top and from top to bottom of the lever 8 around its axis 9. This alternative rotation causes an alternating vertical displacement of the piston 5. In the position represented in FIG. 1, the piston 5 is in its lowest position, slightly above the opening 15; the highest position of the piston 5 is shown in dotted lines in 5 ', this position corresponding to the position 8' of the lever 8.

When the piston 5 rises in the filling tube 3, the liquid substance 18 is sucked through the pipe 16 into the body of the tube 3. As soon as the piston 5 begins to descend, the liquid substance is pushed into the calibrated tube 2. Indeed, the valve 38 prevents any backflow of substance in the pipe 16 towards the reservoir 17.

The circulation of the coolant in the enclosure 19 causes intense cooling and freezing of the substance occupying the interior volume of the tube 2. The coolant rant can be, for example, at a temperature of the order of -20 ° C.

This cooling is sufficiently vigorous that, under the action of the pressure applied from top to bottom by the piston 5 on the upper level of the substance contained in the tube 3, a continuous vertical bead 40 of frozen substance forms under the tube. calibrated 2. The sliding of the bead on the internal wall of the tube 2 is facilitated by the presence of the covering 37.

When the lower end of the cord 40 reaches the light beam 30, part of the energy of this beam is diffused or reflected by the cord 40. The illumination of the receiver 33 therefore decreases, which causes a reduction in the amplitude of the electrical signal delivered by the receiver 33. The circuit 34 reacts to this reduction in amplitude by controlling the triggering of a laser pulse. The laser energy concentrated at point 26 causes the cord 40 to break at this point. A fragment of length 32 is detached from this cord and falls into the container 36.

Of course the interior volume of the tube 3 is capable of storing a quantity of substance sufficient to obtain the successive detachment of the cord 40 from a plurality of identical fragments during a single descent of the piston 5. These fragments are then received respectively in a plurality of containers such as 36 carried by a conveyor belt moving transversely with respect to the axis 27.

It should be noted that it is possible to obtain a plurality of fragments of the same length without the assistance of the tracking device 28-29-33-34. Indeed, on the one hand the profile of the cam 10 can be determined so that the running of the cord 40 leaving the tube 2 takes place at constant speed and on the other hand the laser generator 23 can be controlled to emit a sequence of laser pulses at a constant repetition rate. Under these conditions, knowing the speed of travel, the emission rate of the laser generator is chosen to obtain the desired length 32 of the fragment.

The very high energy density caused by the concentration of the laser beam makes it possible to achieve a clear cut in the cord 40 and very high precision over the length 32 of the fragment, that is to say over the volume of the dose to be deposited. in the container. It should be noted that it is possible to further increase the dosing precision by using as a focusing optical system a cylindrical lens arranged to concentrate the energy of the beam along a segment cutting the cord 40 perpendicularly to its axis 27.

When the accuracy requested on the dose to be deposited in the container is less, it is also possible to cut the cord 40 using known mechanical devices, for example using two knives not shown, arranged parallel to the one to the other in a horizontal plane on either side of the cord 40, these knives being controlled to move in order to come into contact on their cutting edge along a straight line cutting the axis of the cord 40. It is also possible to produce cutting the cord 40 by thermal means, for example using a rectilinear conducting wire brought to high temperature by passing a current, this wire being moved in a horizontal plane cutting the cord 40.

The fragment of frozen substance deposited in the container 36 gradually heats up in contact with the ambient air and is therefore after a certain time again in the liquid state.

Thanks to the oven 35 shown in FIG. 1, it is possible to reheat the fragment during its fall, this fragment then being in the liquid state when it arrives in the container 36.

Of course, such heating can be obtained more generally by any known thermal means, and in particular using an infrared radiation generator.

Reheating the fragment before it arrives in the container may be absolutely necessary when the container 36 is very small and the fragment is relatively long. In fact, in this case the entire length of the frozen fragment cannot be accommodated in the internal volume of the container and part of the substance risks flowing out of the container when the fragment warms up.

Claims (13)

1. Method for depositing in a container a predetermined dose of a liquid substance, consisting first of all in taking a sample of this substance in a tubular piece arranged vertically above the container, characterized in that it then consists to cool a lower part of the tubular part, this lower part being a calibrated tube, - to apply a vertical pressure directed downwards on the upper level of the substance taken from the tubular part, the cooling being intense enough so that, under the influence of said pressure, a continuous vertical bead of frozen substance is formed under the calibrated tube - And to cut the cord so that a fragment of predetermined length detached from the cord is received by gravity in the container, this fragment constituting after liquefying said predetermined dose. 2. Method according to claim 1, characterized in that it further consists in heating the detached fragment of the cord so that it arrives in the liquid state in the container. 3. Device for depositing in a container a predetermined dose of a liquid substance, comprising a tubular piece placed vertically above the container and means for taking a sample of this substance from the tubular piece, characterized in that - the lower part of the tubular part consists of a calibrated tube and that it further comprises - means for cooling the calibrated tube, - Means for applying a vertical pressure directed downwards on the upper level of the sampled substance, these means acting simultaneously with said cooling means to form under the calibrated tube a continuous vertical bead of frozen substance - And means for cutting the cord so as to detach a fragment of predetermined length of the cord, this fragment, received by gravity in the container, constituting after liquefaction said predetermined dose. 4. Device according to claim 3, characterized in that it further comprises means for heating the fragment detached from the cord, these means being arranged on the path of the fragment between the cord and the container. 5. Device according to claim 3 characterized in that said means for cutting the cord comprise a generator of a laser beam and an optical system for concentrating this beam on the cord. 6. Device according to claim 5 characterized in that said means for cutting the cord so as to detach a fragment of predetermined length further comprises a generator of a light beam cutting the axis of the cord at a point located below the laser beam concentration zone and distant from this zone of said predetermined length, an electro-optical receiver arranged to receive the light beam and a circuit for processing the electrical signal delivered by the receiver, this circuit being connected to said laser generator for controlling the triggering of a pulse from this generator when the amplitude of this signal decreases, this reduction in amplitude being caused by the interception of the light beam by the lower end of the cord. 7. Device according to claim 5, characterized in that said optical system is constituted by a cylindrical lens capable of concentrating the beam along a segment perpendicular to the axis of the bead. 8. Device according to claim 3, characterized in that the internal cylindrical surface of the calibrated tube is coated with a layer of a material capable of facilitating the sliding of the frozen substance when said pressure is applied. 9. Device according to claim 3, characterized in that said cooling means comprise an enclosure surrounding the calibrated tube and means for circulating in this enclosure a refrigerated fluid. 10. Device according to claim 3, characterized in that the tubular part comprises in its upper part a filling tube in communication with the calibrated tube and whose internal diameter is greater than that of the calibrated tube and that said means for taking a sample of the substance in the tubular part comprise a piston capable of sliding vertically in the filling tube. 11. Device according to claim 10, characterized in that said means for applying a vertical pressure on the upper level of the substance withdrawn are means for applying said pressure on the piston. 12. Device according to claim 4, characterized in that the heating means of the fragment comprise a vertical tubular oven. 13. Device according to claim 4, characterized in that the heating means comprise an infrared radiation generator.

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