DD290595A5 - METHOD AND DEVICE FOR VOLUMEOUS DOSING OF LIQUIDS - Google Patents

Abstract

The invention relates to a method and a device for volume-correct metering in the microliter and Ultramikroliterbereich. Fields of application are the clinical-chemical laboratories, but also water management and agriculture. The task was to ensure that the metering rate does not exert any negative influence on the volume accuracy. In the method, the pre-dosed liquid is passed into the fluid skin formed at the outlet opening of the dosing cannula and set in defined oscillations. The device for implementing the method has a vibration generating element on the canoe, which has means for controlling the intensity of vibration. {Dosing, true to volume; Microliter, ultramicroliter range; Fluid, predosed; Fluessigkeitshaut; vibration; Schwingungsintensitaetssteuerung}

Description

For this 2 pages drawings

Field of application of the invention

The present invention relates to a method and apparatus for volume correct dispensing of liquids in the microliter and ultramicroliter range.

It improves the technically conventional discharge of the liquids from one or more piston-cylinder systems towards a volume-correct dosage of smallest volumes which are in or below the size of a gravitational field of self-dissolving drop of the corresponding liquid.

Characteristic of the known state of the art

The dosage of smallest amounts of liquid is made mainly according to the principle of volume displacement. Technically realized are two ways to dose volumes that do not want to be detached from the metering tip due to their small size

At the first possible working principle, z. B. after implementation in EP Patent No. 0C41318, the volume to be dispensed is slowly expelled from the metering orifice by displacement, and the operator places it in the desired vessel, the metered volume being affected by the adhesive forces between the liquid and the vessel Dispensing tip triggers.

In the second possible working principle, e.g. according to DE patent no. 2658486, the liquid to be metered on with motor power

accelerates a certain speed. Upon reaching the preset Verdunängunysvolumen is the

Ejection process braked jerkily. According to the geometric dimensions of the cannula, the through the Piston motion controlled speed drain and fluid specific characteristics such as Surface tension and viscosity ruptures the metered amount of fluid during this braking process. Both technically realized working principles show in the quality characteristics of a liquid dosage, volume correct Dosage with low scattering of the individual volumes, the following disadvantages. Devices of the first type are in terms of volume accuracy and scattering of the influence of the operator Deposition of the leaked from d.ir dosing volume depends. \ This disadvantage is overcome by the realized in the second working principle free storage of the liquid to be dispensed so

that for volume over 100 microliters a dosage with satisfactory characteristics is technically realized.

However, if the volume to be dosed comes in or below the order of magnitude of the dosing tip hanging in the gravitational field Dropping, an abrupt braking operation is necessary to achieve a defined tearing de 'liquid. The imprinted Velocity control in the metering of volumes in and below drop size therefore consists of a Acceleration process to the highest possible speed values of the liquid column and a jerkartigon deceleration

together. The necessary for the defined deceleration of the liquid column braking is in practice either by

Travel against fixed stops or realized by extremely short-term stop operations in stepping motor drives. By this procedure, the quality index is scattering for dosages of about 20 microliters down below about 0.5%,

based on the mean value.

The imprinted for the defined tearing of the droplets velocity control of the dosing process, however, shows that the

second quality characteristic, the volume accuracy, with otherwise constant conditions due to technical reasons,

small changes in the speed control is strongly affected.

With an arrangement, technically realized as a motor-driven dosing with fixed stops in the metering and the Connection of dosing (Dosierkanüle) and piston-cylinder system in a technically conventional manner by accordingly

dimensioned hose or cannula lines, whereby valve assemblies can be interposed, was the

described above influence of technically caused minor changes on the quality parameters.

Work was carried out with aqueous solutions and with a fixed volume of 20 microliters. While the quality characteristic scattering in such measurement series remains below the value to be guaranteed, the Quality characteristic Volume accuracy as a percentage deviation of the mean value of the measuring series from the nominal value to about 1%

affected. However, this means influencing this quality characteristic in the order of magnitude of the guaranteed value.

These findings obtained in clinical practice and laboratory investigations are explained by the chaotic behavior of the patients

flowing liquid when flowing and deflecting in their spanned in the metering opening curved surface.

When handling the laminar flowing from the cannula liquid in their spanned in the metering opening surface

the liquid is forced to the turbulent envelope forcibly. In this process, the chaotic

Enforce the behavior of flowing liquids. This process, which occurs during each dosing process, has a disruptive effect on volumes in droplet size and below

an influence on the quality index volume accuracy in the desired order of magnitude.

In other words, the mean of a series of measurements is technically unavoidable changes in the Speed control of the dosing process at drop size already affects about up to one percent. This quality

However, this corresponds to the target figure for the entire dosing process including technologically tolerated limits for the production of dosing.

Object of the invention

With the method and the associated device according to the invention a volume-correct dosage of volumes under drop size with low consumption of reagents and impeccable quality characteristics with user-specific accuracy is achieved without great technical effort and an economic operation in diosen volume ranges are guaranteed.

Explanation of the essence of the invention With '' experience and device to. oil-correct dosage to the described in the prior art, physically

conditional influencing of the quality characteristic Volume accuracy with volumes in and under drop size can be reduced by suitable technical measures.

It was also the task before to exclude operator error from the outset and to ensure that the dosing

has no negative influence on the volume accuracy of the dosage.

The basic idea of the invention is that by means of suitable technical measures, the physically induced chaotic

from the outside with a stochastic process is superimposed, so that the chaotic correlation between

Flow rate and volume accuracy is broken in the volume range described. According to the invention the object is achieved in that vibrations in the, spanned in the opening of the dosing,

curved fluid surface to be energized in this vibrating fluid skin, which forms part of the dosing

Volume, which is conveyed in a conventional manner pre-dosed volume and according to the Speed control of the dosing process Defines the liquid skin and the pre-dosed volume absorbed by it

be demolished, during the entire period until the demolition of the metered volume the

Liquid surface is kept in continuous oscillations. It appears as a favorable variant that the oscillation perpendicular to the direction of movement of the liquid on the Liquid volume is directed. As a stochastic process, the vibrations that act on the clamped in the cannula opening, curved Liquid surface be imprinted, so that the turbulent envelope of the laminar flow of the metered liquid

is superposed with a zufä''igen component.

The method is realized according to the invention by a device, characterized in that the cannula-like Dosleröffn.ung by means of suitable fasteners a vibration-generating element is attached, the over Has devices for controlling the acting on the surface of the liquid vibration intensity. As a device for controlling the vibration intensity acting on the liquid surface, slidable

the oscillatory system mountable and clampable mountings for the cannula-like metering opening, devices for influencing the electromechanical feedback conditions, adjustable technical means of the

Impulse transmission from the oscillating system to the cannula-like metering opening, in particular via screw connections

adjustable, resilient couplings serve.

The vibration generating element may be an electromechanical or a piezoelectric vibrator. The exciter frequency is preferably between 100 Hz and 10 kHz. The vibrations generated by the vibration generating Eloment act with an intensity that Breaking apart of the liquid surface spanned in the metering opening under the influence of these vibrations

prevented.

The method and the device according to the invention will become apparent on an embodiment and the attached figures

explained in more detail.

Embodiment show

Fig. 1: Overview of the dosing Fig. 2a-d: Details of the processes at the metering in the individual process steps Fig. 1 is the important for the understanding technical overview representation of the method and apparatus according to the invention. Starting point for the realization of the dosing of a liquid is a mostly technically realized piston 1-cylinder 2- System. The liquid 3 is displaced by the piston 1 in the cylinder 2, conveyed to the metering opening 4 and through this

pushed out. The connection of metering 4 and piston 1 cylinder 2 system is carried out in a technically conventional manner by appropriately sized hose or cannula 5, whereby valve assemblies 6 may be interposed. The movement of the piston 1 is preferably achieved via a motor-driven coupling, shown symbolically in FIG. 7, via the piston rod 8.

The size of the ejected volume is determined by a limitation of the piston movement between mechanical or

determined by electronic attacks. These stops are symbolically represented by 9.

A per se technically known electromechanical vibration system 10 is now attached to the cannula 5,

that the mechanically oscillating part can impart vibrations to the metering opening 4 via the cannula conduit 5. The

Use of a piezoelectric vibrator is also conceivable for this purpose. As a technically suitable means for adjusting the vibration intensity of the clamped in the metering 4 Fluid skin was a longitudinally displaceable on the cannula 5 and clamped Aufnahmeelemont 11 of

electromechanical vibration sensor 10 is used, with a surrounding the cannula 5, not shown

Sleeve, the vibrations generated are directed to the Dosieröffnug 4. By a longitudinal displacement of this Receiving device 11 on the cannula 5 is the intensity of the vibrations in the curved liquid surface

adjustable.

With such an arrangement, technically realized as a motor-driven metering with mechanical hard stops in Dosing, was the above-described influence of technically slight changes in speed on the Quality parameters volume accuracy examined. The connecting tubes and cannulas 5 were made of polyethylene

an inner diameter of 1.2 mm, the geometric dimensioning of the metering 4 was in the inner diameter

between 0.3 and 0.5mm with a transition length of cannula diameter to dosing of 4 to 6mm.

According to the essence of the invention, the volume of liquid predosed by the piston 1-cylinder 2 system will now become one

imprinted perpendicular to the flow direction vibration. This vibration is controlled by an external, at the

Dosing cannula attached vibrator 10 excited. The intensity of the vibrations to be recorded shall be adjusted by the technical measures specified so that the

in the metering opening 4 spanned liquid surface is not torn under the influence of the imposed vibrations, but can completely absorb the metered volume.

Technically also suitable appear circuit measures for electrical adjustment of

electromechanical feedback conditions or piezoelectrically excited vibrations, that is, a primary control of the excited in the vibrating system 10 intensity.

A supported in a holding device, spring-loaded pressure device controlled by the acting spring force Transmission of the vibrations generated in the vibrating system 10 to the cannula 5 is to control the intensity of the Vibrations of the clamped in the metering 4 liquid skin also conceivable; while the acting Spring force can be adjusted by screw connections. . The described intensity control devices can be used both in a conventional handpiece for Needle holder can be integrated as especially when used in measuring stations designed as individual modules

become.

The frequency of the vibrations to be recorded should be between 100 Hz and 10 kHz. The optimal excitation frequency of the oscillating system is determined by the specific application and is influenced by the geometric conditions at the metering, the size of the volume to be dispensed, the viscosity of the liquid to be dispensed and the speed of the dosing process. For adapting the excitation frequency to the specific dosing task, the following tendencies should be used: a reduction of the volume to be dosed requires a higher exciter frequency; when enlarging the spanned, curved liquid surface by geometric dimensioning is optimized by lowering the excitation frequency. A functional relationship of these tendencies can not be produced due to the chaotic nature of the dosing process.

In the experiment, under the experimental conditions given above, we successfully worked with frequencies between \ 500 Hz and 1 kHz. For the generation of the excitation frequency suitable circuitry measures are provided, which must include in addition to the electrical generation and eventual amplification of the Erregorfrequenz also circuit measures for switching the excitation frequency according to dom current state in the dosing process. They are realized in the symbolically specified control unit 12.

By these measures, the vibrating system 10 is to be activated before the beginning of the dosing process and to remain activated during the duration of the dosing process. Experimentally, this problem has been solved by appropriate electrical switches on the metering process controlling mechanical cam of the incised Festvolumendosierers. In order to understand the basic process steps, the processes at the metering orifice 4 are shown in detail in FIGS. 2a-d. Fig. 2 a shows the conditions in the metering 4 in the rest ezustand. In the metering 4, the curved liquid skin 13 is clamped, which forms inevitably at the interface of air and liquid 3. Depending on the balance of forces between wetted wan j and free liquid surface, it is stretched concavely or convexly .. The external oscillating device is switched on before the metering process begins Time points in different positions, whereby according to the invention the metering process is superimposed on a stochastic component.

If the liquid 3 .'un displaced by a movement of the piston 1, it flows in this process in the clamped liquid skin 13. There, the inflowing liquid flow is deflected by the tension of the surface skin, it comes to the turbulent envelope of the liquid, the chaotic nature of the dosing process justified. The spanned liquid skin 13 inflates slowly by receiving the inflowing liquid 4. It vibrates according to the vertically imposed vibrations to their rest position. This progressive process is shown in Figures 2 b and 2 c, wherein the different layers A and B symbolize different phases of vibration. After taking up the metered volume, the inflated liquid skin 13 finally breaks away from the metering opening 4 due to the continuous oscillation effect by terminating the metering process. This condition is illustrated in Fig. 2d. This completes a dosing process.

Claims (9)

A method for volume correct metering, wherein the metered liquid is accelerated by engine power to a certain speed and decelerated upon reaching mechanical or electronic stops or ejection process, characterized in that vibrations are excited in the, spanned in the opening of the dosing cannula, curved liquid surface, in this vibrating liquid skin, which forms part of the volume to be dispensed, in a conventional manner predosed volume is conveyed and according to the speed control of the dosing process liquid skin and absorbed by her, predosed volume defined to be brought to break, wherein during the entire period to Outline of the dosed volume the liquid surface is kept in continuous oscillations. 2. The method according to claim 1, characterized in that the vibration is directed perpendicular to the direction of movement of the liquid to the liquid volume. 3. A device for the realization of the method for correct volume dosing of liquids, consisting of a piston-cylinder system with cannula-like dosing, wherein the volume to be dosed is promoted by a, powered by appropriate devices between mechanical or electronic attacks piston in the dosing, characterized in that at the cannula-like metering opening by means of suitable connecting elements, a vibration-generating element is mounted, which has means for controlling the acting on the liquid surface, vibration intensity. 4. Apparatus according to claim 3, characterized in that for controlling the force acting on the liquid surface vibration intensity on the cannula-like dosing slidably arranged and clampable mounting of the oscillatory system is used. 5. Apparatus according to claim 3 or 4, gekannzeichnet in that the force acting on the liquid surface vibration intensity is controlled by devices that affect the electromechanical feedback conditions electrically. 6. Apparatus according to claim 3 or 4, characterized in that the force acting on the liquid surface vibration intensity is controlled by adjustable technical means of impulse transmission from the vibration system to the cannula-like metering, in particular by screw adjustable, resilient coupling. 7. Device according to one of claims 3 to 6, characterized in that the vibration generating element is an electromechanical oscillator. 8. Device according to one of claims 3 to 6, characterized in that the vibration-generating element is a piezoelectric oscillator. 9. Apparatus according to claim 3 to 8, characterized in that the excitation frequency of the vibration-generating elements is preferably between 100Hz and 1OkHz.