DE102013111800A1 - Precision metering device with expandable volume chamber - Google Patents

Abstract

The invention relates to a precision metering device for metering a fluid, comprising a resilient volume chamber (VK) with an inlet valve (Ve) and an outlet valve (Va) and a control device for actuating the inlet valve (Ve) and the outlet valve (Va). When the control device opens the inlet valve (Ve) and closes the outlet valve (Va), the volume of fluid in the volume chamber (VK) increases due to a fluid pressure provided by an upstream compressor and expands the elastic volume chamber (VK). When the control device closes the inlet valve (Ve) and opens the outlet valve (Va), the elastic volume chamber (VK) contracts and discharges the fluid via the opened outlet valve. The volume of fluid discharged via the outlet valve (Va) can be determined on the basis of a surface shape change of the elastic volume chamber (VK). According to the invention, the volume chamber (VK) is encased with a capacitive strain sensor and the surface shape change can be determined on the basis of the capacitance change of the capacitive strain sensor.

Description

The invention relates to a metering device and in particular, but not exclusively, to a precision metering device with an expandable volume chamber according to the preamble of claim 1.

• – Vereinigung der Vorteile von präzisen Fördereinrichtungen und der Größe von einem Infusionsreservoir.
• – Möglichkeit der Flusskontrolle nah am Patienten, insbesondere durch Nutzung des Schlauchs als Energieleiter, unter Berücksichtigung des Kompressordrucks und der damit einhergehenden Miniaturisierbarkeit.
• – Etablierung einer Präzisionsmessung, die einfacher, billiger und genauer ist als vergleichbare Präzisionsfördermechaniken, sowie Etablierung eines Regelkreises.
• – Möglichkeit einer extrakorporalen Zumischung, d.h. der Förderung in beide Richtungen, oder einer sequentiellen Infusion durch Unabhängigkeit vom Kompressor und Verwendung kleinster Schlauchvolumina.
• – Ermöglichung von Mehrkammersystemen.

The invention relates to the field of precision metering units that draw their (conveying) energy, for example, from an upstream compressor and are integrated in a control loop. The essential characteristics of this construction are:

• - Combining the advantages of precise conveyors and the size of an infusion reservoir.
• - Possibility of flow control close to the patient, in particular by using the hose as an energy conductor, taking into account the compressor pressure and the associated miniaturization.
• - Establishment of a precision measurement that is simpler, cheaper and more accurate than comparable precision conveyor mechanisms, as well as establishment of a control loop.
• Possibility of extracorporeal admixture, that is to say delivery in both directions, or sequential infusion by independence from the compressor and use of smallest tubing volumes.
• - Enabling multi-chamber systems.

The prior art precision metering units have the disadvantage of requiring special metering / metering chambers, e.g. "Balloon" or "membrane double chamber". For reasons of hygiene, however, it would be advantageous to be able to carry out all measuring elements as single-use products that are used only for one patient and can then be disposed of.

The object of the invention is to transfer the known principle of the volume chambers on common infusion tubes, which can be used as disposables.

This object is achieved by the precision device according to claim 1. Preferred embodiments of the invention are the subject of the dependent claims.

The invention is based on the following consideration. The principle of Präzisionsdosiervorrichtungen should be easily transferred to disposable items. For this purpose, in the customary disposable articles, i. The surface of the current infusion tubing is structured accordingly, for example by spraying suitable structures for measuring the relevant state variables. On the other hand, instead of a tube modification, the precision metering device according to the invention can be pulled over the infusion tube.

A precision metering device according to the invention for metering a fluid has an elastic volume chamber with an inlet valve and an outlet valve and a control device for actuating the inlet valve and the outlet valve. When the controller opens the inlet valve and closes the outlet valve, the volume of fluid in the volume chamber increases due to a fluid pressure provided by an upstream compressor, and the elastic volume chamber expands, and when the controller closes the inlet valve and opens the outlet valve, the elastic volume chamber contracts and dispense the fluid through the opened outlet valve. The volume of fluid delivered via the outlet valve can be determined on the basis of a surface shape change of the elastic volume chamber. According to the invention, the volume chamber is encased with a capacitive strain sensor and the surface shape change can be determined on the basis of the capacitance change of the capacitive strain sensor.

• – der kapazitive Dehnungssensor zwei flexible gummiartige und elektrisch leitfähige Schichten sowie eine ebenso flexible, aber nicht leitfähige Isolator-Schicht der Dicke d dazwischen umfasst, so dass durch die drei funktionalen Schichten ein Zylinderkondensator mit variablem Radius gebildet wird;
• – die drei Schichten als ein mindestens dreischichtiges gummiartiges Schlauchstück über ein Infusionsschlauchsegment gezogen werden;
• – eine innere Gleitschicht und/oder eine äußere Isolatorschicht auf beiden Seiten des Kondensators vorgesehen sind.

Preferred embodiments of the invention have as one or more of the following features:

• The capacitive strain sensor comprises two flexible rubber-like and electrically conductive layers and an equally flexible but non-conductive insulator layer of thickness d therebetween such that a variable radius cylinder capacitor is formed by the three functional layers;
• - The three layers are drawn as an at least three-layered rubber-like piece of tubing over an infusion tube segment;
• - An inner sliding layer and / or an outer insulator layer are provided on both sides of the capacitor.

The invention has the following advantages, among others. Already existing infusion tubes can be retrofitted in a simple manner by their surface is structured accordingly, for example by Spraying suitable structures. Hose modification is not necessary when the capacitive strain sensor is pulled over the metering chamber segment of the hose.

In addition, the precision metering device according to the invention enables the precise detection of changes in volume in, for example, infusion tubes or tubular disposable / reusable articles, whereby it could also be used directly under the peristalsis of a peristaltic pump. It also enables reliable non-invasive volumetric flow measurement. Essentially, a commercial chip is sufficient for the underlying measurement technology. A single measurement allows the determination of the volume change; Thus, this measurement accomplishes the measurement of the ("middle") entire segment surface in one go.Therefore, even a chip enables two-digit measuring frequencies, which means that a complex measuring mechanism is not required because with them the precision metering device according to the invention only has to be pulled over in order to be able to carry out the underlying measuring method.

Further features and advantages of the invention will become apparent from the following description of preferred embodiments, reference is made to the accompanying drawings.

1 shows the functional sequence of a known Präzisionsdosiervorrichtung.

2 shows an embodiment of the Präzisionsdosiervorrichtung invention in a perspective view in the sliced.

In general, the operation of a precision metering device is known. When the inlet valve Ve (and closed outlet valve Va) of the metering / measuring chamber VK is open, the compressor pressure pushes infusion liquid from a reservoir into the chamber VK. The disposable article expands in this area, changing the shape of its surface. Now the inlet valve Ve is closed and awaited an approximately vibration-free state of equilibrium. The volume of the measuring chamber VK is measured. This is done by determining the surface shape of this hose segment (or its deformation). Now, the exhaust valve Va is opened.

Thus, the strained measuring chamber wall pushes the fluid out of the chamber VK in the direction of the patient. Now, the exhaust valve Va is closed and a state of equilibrium in the chamber is awaited. The re-measurement of the surface (ie the volume) allows the control loop to accurately determine the amount delivered in this cycle. This is the difference between the two volume measurements.

The operation of the Präzisionsdosiervorrichtung is to better understand the invention as a control loop in the following briefly with reference to 1 explained.

First, the system is in equilibrium, step " 0 ".

In step 1 an intake valve Ve is opened. The compressor pressure pushes liquid under extension of the measuring chamber VK in this.

In step 2 If the inlet valve Ve is closed, the shape and thus the volume of the chamber VK are determined in equilibrium.

In step 3 the exhaust valve Va is opened. The tension in the chamber wall pushes fluid out of the measuring chamber (VK) towards the patient.

In step 4 the exhaust valve Va is closed. In equilibrium, the shape and thus the volume of the chamber VK are determined.

On the basis of the volume difference between steps two and four, the conveyed quantity can be determined.

In 2 an embodiment of the precision metering device according to the invention is shown. In this embodiment, the precision metering device is an at least three-layer rubbery piece of tubing 5 , eg via an infusion tube segment 6 can be pulled. Between two very flexible rubbery and highly conductive layers 7 is an equally flexible but non-conductive Insulator layer 8th the thickness d. The insulator layer is thin. All three functional layers together form a cylindrical capacitor of variable radius. Its length is denoted by l below. In the following, the shortest (radial) distance between the hose center and the insulator layer is referred to as radius r. As will now be shown, the capacitance of the precision metering device with a constant distance d of the conductive layers varies to a good approximation linearly with the radius r, ie also linearly with the radius of the underlying infusion tube segment. From this it is easy to determine volume changes of the infusion tube segment. Of course, additional layers are conceivable and useful. Thus, an inner "sliding layer" and an additional outer insulator layer could be useful.

The precision dosing device is pulled over the dosing / measuring area of the infusion tube. The capacity of the precision metering device is measured to determine the volume delivered per cycle reliably and non-invasively. The capacity is as follows:

The Taylor order of first order (0 + 1) yields:

Under the given assumption of a negligible insulator layer thickness d, this is simplified in a good approximation to:

That the capacity of the precision metering device is, to a good approximation, linear with the radius r; the line slope is proportional to l / d. A thin insulator layer thus favors the measurement.

In a comparison made between the exact capacitance values of a probable observation area and the above linear approximation, good agreement is shown, in particular in the slope which is decisive for the method. In particular, here the excellent linearity also shows for the exact calculation.

The quality of the linearity in turn depends decisively on the insulator layer thickness d. In addition, larger radii have a favorable effect.

Calculations show that the deviation from the linearity at thicknesses d below one tenth of a millimeter is even in the per thousand range.

With the same dimensioning, it can also be shown that, as expected, a small insulator layer thickness also has a favorable effect on the measurement interval.

The measurement of capacities in the required Picofaradbereich is nowadays with very good accuracy simply accomplished by cheap commercial ready-chips. An example is the AD7745 / AD7746 (Analog Devices) with a preferred measuring range of 4 picofarads. This chip can resolve capacity changes down to the Attofarad range (!) And convert it into digital values.

The invention is not limited to the illustrated embodiments. In principle, the concept of the further development of a precision metering device proposed in this application adapts the previous advantages of metering devices to existing infusion line systems. The measurement of the tubing volume in the measuring / dosing range can be accomplished here by numerous common techniques with arbitrary precision and almost any speed, an example of which is the laser scan.

LIST OF REFERENCE NUMBERS

"0"

System in balance

1

Inlet valve is opened. The compressor pressure presses liquid under extension of the measuring chamber.

2

Inlet valve is closed. In equilibrium, the shape and thus the volume of the chamber are determined.

3

Exhaust valve opens. The tension in the chamber wall pushes fluid out of the measuring chamber towards the patient.

4

Exhaust valve is closed. In equilibrium, the shape and thus the volume of the chamber are determined.

5

three-layered rubber-like piece of hose

6

Infusion tube segment

7

conductive layer

8th

Insulator layer

d

thickness

r

radius

l

length

VK

volume chamber

Ve

intake valve

Va

outlet valve

Claims (4)

A precision metering device for metering a fluid having a resilient volume chamber (VK) with an inlet valve (Ve) and an outlet valve (Va) and a control device for actuating the inlet valve (Ve) and the outlet valve (Va), wherein when the control device controls the inlet valve (Ve ) and the exhaust valve (Va) closes, the volume of fluid in the volume chamber (VK) increases due to a fluid pressure provided by an upstream compressor, and the elastic volume chamber (VK) expands, and when the control device closes the intake valve (Ve) and the exhaust valve (Va) opens, the elastic volume chamber (VK) contracts and discharges the fluid via the opened outlet valve, and wherein the volume of fluid discharged via the outlet valve (Va) is determinable based on a surface shape change of the elastic volume chamber (VK); characterized in that the volume chamber (VK) provided with a capacitive strain sensor, in particular sheathed, is; and the surface shape change is determinable based on the capacitance change of the capacitive strain sensor. Precision metering device according to claim 1, characterized in that the capacitive strain sensor comprises two flexible rubber-like and electrically conductive layers ( 7 ) as well as an equally flexible but non-conductive insulator layer ( 8th ) of a predetermined thickness (d) therebetween so that through the three functional layers ( 7 . 8th ) a variable-radius cylinder capacitor (r) is formed. Precision metering device according to claim 2, characterized in that the three layers ( 7 . 8th ) as an at least three-layer rubber-like piece of tubing over an infusion tube segment ( 6 ), which serves as an elastic volume chamber, are pulled. Precision metering device according to claim 2 or 3, characterized in that an inner sliding layer and / or an outer insulator layer are provided on both sides of the capacitor.

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