Arrangement and method for determining a stopper position

Abstract

The invention relates to an arrangement for determining a position (x) of a stopper relative to a container in a drug delivery device, comprising an acoustic source configured to emit an acoustic signal and an acoustic sensor configured to detect an acoustic signal, a processing unit for controlling the acoustic source and processing the detected acoustic signal for determining characteristics of the acoustic signal correlated with the position (x) of the stopper. Furthermore, the invention relates to a method for determining a position (x) of a stopper relative to a container in a drug delivery device, the method comprising the steps of emitting an acoustic signal from an acoustic source, detecting an acoustic signal caused by the emitted acoustic signal by means of an acoustic sensor, and processing the detected acoustic signal for determining characteristics of the acoustic signal correlated with the position (x) of the stopper by means of a processing unit.

Claims

1. A drug delivery device with a container defining a cavity for a drug and a stopper for proximally delimiting the cavity and displacing the drug from the cavity, the drug delivery device further comprising an arrangement for determining a position (x) of the stopper relative to the container, the arrangement comprising an acoustic source configured to emit an acoustic signal and an acoustic sensor configured to detect an acoustic signal, a processing unit for controlling the acoustic source and processing the detected acoustic signal for determining characteristics of the acoustic signal correlated with the position (x) of the stopper, wherein the acoustic source is aligned to emit the acoustic signal into a resonance volume, which is defined in one spatial dimension by the position of the stopper, wherein the processing unit is configured to vary the frequency (f) of the emitted acoustic signal within a pre-determined frequency range, wherein the processing unit is configured to detect a harmonic (f.sub.1(x), f.sub.2(x), f.sub.3(x), f.sub.4(x)) of a resonance frequency f.sub.k characteristic for the resonance volume related to the position (x).

2. The drug delivery device according to claim 1, wherein the acoustic source is aligned to emit the acoustic signal through a proximal opening of the container towards the stopper, wherein the processing unit is configured to control the acoustic source so as to emit a coded acoustic wave (U) and to determine a delay or phase shift of the detected acoustic wave related to the position (x).

3. The drug delivery device according to claim 2, wherein the acoustic wave (U) is an ultrasonic wave (U).

4. The drug delivery device according to claim 2, wherein the acoustic source and the acoustic sensor are integrated in a sound converter operatively switchable to act as either the acoustic source or the acoustic sensor.

5. The drug delivery device according to claim 1, wherein the resonance volume is at least partially defined within a proximal end of the container.

6. The drug delivery device according to claim 1, wherein a tube section with essentially the same internal diameter as the container is arranged proximally adjacent the container for at least partially defining the resonance volume.

7. The drug delivery device according to claim 1, wherein the pre-determined frequency range is selected so as to match at least part of a range of linear frequency response of the acoustic source.

8. A method for determining a position (x) of a stopper relative to a container in a drug delivery device, the method comprising the steps of: aligning an acoustic source to emit an acoustic signal into a resonance volume, which is defined in one spatial dimension by the position of the stopper; emitting the acoustic signal from an acoustic source, wherein the frequency (f) of the emitted acoustic signal is varied within a pre-determined frequency range; detecting, by an acoustic sensor, an acoustic signal caused by the emitted acoustic signal, wherein a harmonic (f.sub.1(x), f.sub.2(x), f.sub.3(x), f.sub.4(x)) of a resonance frequency f.sub.k characteristic for the resonance volume related to the position (x) is detected; and processing the detected acoustic signal for determining characteristics of the acoustic signal correlated with the position (x) of the stopper by means of a processing unit.

9. The method according to claim 8, wherein the acoustic source is aligned to emit the acoustic signal through a proximal opening of the container towards the stopper, wherein the acoustic source is controlled so as to emit a coded acoustic wave (U) and wherein a delay or phase shift of the detected acoustic wave related to the position (x) is determined.

10. The method according to claim 9, wherein the acoustic wave (U) is an ultrasonic wave (U).

11. The method according to claim 9, wherein the acoustic source and the acoustic sensor are integrated in a sound converter which is operatively switched to act as either the acoustic source or the acoustic sensor.

12. The method according to claim 8, wherein the pre- determined frequency range is selected so as to match at least part of a range of linear frequency response of the acoustic source.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus, are not limitive of the present invention, and wherein:

(2) FIG. 1 is a schematic longitudinal section of a drug delivery device with an ultrasonic transmitter-sensor-arrangement for determining a stopper position;

(3) FIG. 2 is a schematic longitudinal section of a drug delivery device with a acoustic source and a acoustic sensor for a resonance based determination of a stopper position;

(4) FIG. 3 is a diagram showing an amplitude of the acoustic signal detected by the acoustic sensor depending on the frequency of the acoustic signal;

(5) FIG. 4 is a diagram showing a resonance frequency depending on the stopper position; and

(6) FIG. 5 is a diagram showing a frequency shift of the resonance frequency depending on the stopper position.

(7) Corresponding parts are marked with the same reference symbols in all figures.

DETAILED DESCRIPTION

(8) FIG. 1 is a schematic longitudinal section of a drug delivery device 1. The drug delivery device 1 comprises a cylindrical container 2 defining a cavity 3 for a drug. The cavity 3 is proximally delimited by a stopper 4 which may be translated within the container 2 for displacing the drug from the cavity 3 through a discharge nozzle (not illustrated) arrangeable at a distal end of the container 2. An acoustic source 5 and an acoustic sensor 6 designed as an ultrasonic transmitter-sensor-arrangement are arranged for determining a position of the stopper 4 relative to the container 2 by measuring the distance between the ultrasonic transmitter-sensor-arrangement 5, 6 and the stopper 4. The ultrasonic transmitter-sensor-arrangement 5, 6 should therefore be fixed in position relative to the container 2. The ultrasonic transmitter-sensor-arrangement 5, 6 is operated with a frequency which is non-audible for a human, e.g. in the range between 20 kHz and 400 kHz. The ultrasonic transmitter-sensor-arrangement 5, 6 comprises an acoustic source 5, also referred to as a transmitter and an acoustic sensor 6, also referred to as a receiver. In an exemplary embodiment the ultrasonic transmitter-sensor-arrangement 5, 6 is arranged as a sound converter for minimizing the foot print. The sound converter may be operated as an acoustic source 5 for emitting a coded, e.g. pulsed or modulated ultrasonic wave U and switched to operate as an acoustic sensor 6 after lapse of a pre-determined time window. Within this time window the coded ultrasonic wave U hits the device under test, i.e. the stopper 4, which reflects the ultrasonic wave U so that it can be detected by the acoustic sensor 6. The processing unit 10 then determines the delay or phase shift of the detected ultrasonic wave with respect to the emitted ultrasonic wave U. The time window and the sonic velocity determine a minimum distance, which has to be adjusted between the ultrasonic transmitter-sensor-arrangement 5, 6 and the stopper 4. For an exemplary measuring frequency of 400 kHz the minimum distance would be approximately 20 mm.

(9) Controlling the acoustic source 5 and acoustic sensor 6 as well as coding the ultrasonic wave U, processing the detected ultrasonic wave and determining the distance may be performed by a processing unit 10, which may likewise be integrated in the ultrasonic transmitter-sensor-arrangement 5, 6.

(10) FIG. 2 is a schematic longitudinal section of a drug delivery device 1 with an acoustic source 5 and an acoustic sensor 6 for a resonance based determination of a position of the stopper 4. The drug delivery device 1 comprises a cylindrical container 2 defining a cavity 3 for a drug. The cavity 3 is proximally delimited by a stopper 4 which may be translated within the container 2 for displacing the drug from the cavity 3 through a discharge nozzle (not illustrated) arrangeable at a distal end of the container 2. An acoustic source 5 and an acoustic sensor 6 are arranged for determining a position of the stopper 4.

(11) The stopper 4 in FIG. 2 is shown at a position within the container 2 so that a resonance volume 7 filled with air is defined proximally from the stopper 4 within the container 2. The position of the stopper 4 may be determined by measuring resonances caused by acoustic waves within this resonance volume 7. The resonance volume 7 forms an oscillatory system with a resonance frequency which is characteristic for the size and geometry of the resonance volume 7 according to the laws of Kundt's tube. If Kundt's tube is excited with the resonance frequency a standing wave 8 forms, such that an amplitude of the resonance frequency increases and can be measured by the acoustic sensor 6, e.g. a microphone.

(12) The acoustic source 5 may be controlled by a processing unit 10 to wobble through a defined frequency band, i.e. to emit sound waves with frequencies varying within this frequency band. The sound waves acquired by the acoustic sensor 6 may be analyzed in the processing unit 10 for determining the maximum amplitude and thus the resonance frequency. FIG. 3 is a diagram showing a typical amplitude spectrum |X(f)| of the acoustic signal detected by the acoustic sensor 6 depending on the frequency f of the acoustic signal emitted by the acoustic source 5 into the resonance volume 7. The amplitude |X(f)| has a maximum at the resonance frequency f.sub.k. The position of the stopper 4 can then be determined by equation (1):

(13) $\begin{array}{cc}{f}_k=\left(2k-1\right).Math.\frac{c}{4l},kN,& \left(1\right)\end{array}$

(14) wherein c is the sonic velocity in air, l is the length of the cylindrical resonance volume 7 and k is the harmonic index.

(15) Typically, the stopper 4 of an unused container 2 is positioned at the very proximal end or just a very short distance within the container 2 so that no resonance volume 7 at all or just a very small resonance volume 7 is provided. This would result in a very high resonance frequency f.sub.k, which may be out of the range of the acoustic source 5 and/or the acoustic sensor 6. In order to allow for employing the resonance measuring method even with the stopper 4 positioned at the very proximal end of the container 2, a tube section 9 with essentially or exactly the same internal diameter as the container 2 is arranged proximally adjacent the container 2, so that a resonance volume 7 exists regardless of the position of the stopper 4 (cf. FIG. 2). In an exemplary embodiment the tube section 9 has a length of 10 mm.

(16) FIG. 4 is a diagram showing the resonance frequency f.sub.K depending on the position x of the stopper 4 relative to the proximal end of the container 2. FIG. 4 illustrates the fundamental resonance frequency or first harmonic f.sub.1(x) with k=1, the second harmonic f.sub.2(x) with k=2, the third harmonic f.sub.3(x) with k=3 and the fourth harmonic f.sub.4(x) with k=4.

(17) FIG. 5 is a diagram showing a frequency shift f of the resonance frequency f.sub.k depending on the position x of the stopper 4 when varying the position x by 0.1 mm.

(18) As can be seen in FIG. 5 the change of the resonance frequency f.sub.1(x),f.sub.2(x),f.sub.3(x),f.sub.4(x) for the first, second, third and fourth harmonic f.sub.1(x), f.sub.2(x), f.sub.3(x), f.sub.4(x) between two positions x of the stopper 4 at small distances or positions x of the stopper 4 from the proximal end of the container 2, e.g. x=5 mm, is relatively high. However, according to equation (1) the amount of change f.sub.1(x),f.sub.2(x),f.sub.3(x),f.sub.4(x) decreases with higher distances or positions x of the stopper 4.

(19) In an exemplary embodiment the method for determining the position x of the stopper 4 is performed with the fundamental frequency f.sub.1(x). The acoustic source 5 emits acoustic waves in the frequency range from 0 to 10 kHz. In order to achieve a uniform intensity, the acoustic source 5 should have a linear frequency response at least within the intended frequency band. The acoustic sensor 6 acquires the power amplitude of the sound in the resonance volume 7, which is stored and assigned to the respective frequency f by the processing unit 10. If the generated frequency matches the resonance frequency f.sub.1(x), resonance occurs resulting in an increased power signal detected by the acoustic sensor 6 (cf. FIG. 3).

(20) The aforementioned arrangements and methods may be applied for measuring fill levels in containers such as glass ampoules for dosing liquids, e.g. drugs.

(21) The aforementioned arrangements and methods allow for reducing the required space and part count and to improve handling.