WO2007148361A1

WO2007148361A1 - System for integrity testing of closed containers made of non-conductive material

Info

Publication number: WO2007148361A1
Application number: PCT/IT2007/000231
Authority: WO
Inventors: Alvaro Guidi; Alessandro Spinetti
Original assignee: Federighi Federigo; Federighi Mario; T.I. Engineering S.R.L.
Priority date: 2006-06-21
Filing date: 2007-03-28
Publication date: 2007-12-27
Also published as: ITRM20060326A1

Abstract

The invention relates to a system for controlling defects in closed containers of non-conductive material, comprising: A. a subsystem for dragging the containers; B. two electrodes, connected to an alternating high frequency voltage source, which are applicable on predefinable zones of said containers along a stretch of their passage; C. a subsystem of acquisition of data relevant to the voltage signal which passes through the containers; D. a data elaboration subsystem, characterised in that the data elaboration subsystem carries out the following operations: E. comparison of said voltage signal which passes through the containers with a threshold value SV; F. determination of the presence of defects in the case where the number of exceedings of said threshold value SV is greater than a minimal predefinable number m, the threshold SV being automatically adjusted by the data elaboration subsystem as a function of the values relevant to voltage signal acquisitions between two measurements of two subsequent samples.

Description

SYSTEM FOR INTEGRITY TESTING OF CLOSED CONTAINERS MADE OF NON-CONDUCTIVE MATERIAL

The invention relates to a system for integrity testing of closed containers made of non-conductive material.

More in detail, the invention concerns a system which allows to individuate the presence or the absence of defects in closed containers of nonconductive material, so as to allow discarding the samples during the same production cycle. The system according to the invention is highly reliable since it adapts the evaluation parametres during its working.

It is known from patent JP 95117530 that the exploitation of the simple principle of the electric discharge in the field of detection of seal defects of containers for various products was known since along time. Making reference to herewith enclosed figure 1 , the same patent describes a specific arrangement in the detection of seal defects, in the case where the materials of the container are not resistant to temperature, comprising specific means (18) of cooling of the container (10) surface

(12) portion interested by electric discharge, for example a flow which flows on the test container very close to the electrode (16). Other published patent documents concerns a specific arrangement in the application of the above-mentioned principle to the detection of defects as well, in particular of pinholes.

Document EP 1195599 A1, making reference to herewith enclosed figure 2, concerns a method for the detection of defects in an organic film (21) deposited on the surface of a concrete body (20), the method comprising the measuring of the conductivity of the concrete. To this end, suited conductivity measuring means (10) are used, which comprises two contact electrodes (11 ,12) and a third noncontact electrode

(13) that is isolated with respect to the first two ones via isolating means (14), as well as cannot an oscillator for the application of the sinusoidal voltage of 10-20 V having frequency comprised between 1 and 10 MHz: Once measured the conductivity, indirectly through the organic film (21 ), of the concrete body (20), one applies to the film a defects detector under specific conditions of the concrete. In such a way, by combining the results of the two measurements, one individuates the possible presence of defects. This system uses therefore not two but three electrodes and presupposes preventive measurements of properties of the material enclosed in the containers (in the instance measurement of the concrete substrate). The document WO 82 01418 A1 , with reference to herewith enclosed figures 3, concerns a method for verifying the presence of defects in closed containers (1 ) of isolating material and containing electrically conductive material, the method consisting in positioning the container at a suited distance between the two electrodes (2,3). An alternating voltage difference (4) is applied between the two electrodes, such that to provoke a corona discharge when container defects are absent, or a glow discharge is caused in the case of presence of defects. In the first case, an alternating-current will flow at the frequency, of the order of 10th of KHz, in the second case at the frequency of the order of KHz. As a consequence, the presence or the absence of defects can be determined by observing the frequency component of the current. The document US 4229645 describes a device for detection of holes or cuts or tears that are present on sheets of plastic material, the detection using the principle of electric discharge. Such a device allows to remedy to the detection trouble in the prior art devices, caused by the generation of electrostatic charges in the sheets as a consequence of the sliding of the same. This allows further to remedy to the fact that for a single hole the discharge detection is repeated several times because of the sliding in the proximity of the electrodes and still to the fact that the tears are not defined as holes sequence.

The device allows to filter the electrostatic discharges and to count the discharges due to the presence of defects. As soon as a discharge appears, one counts the subsequent ones. If the number is larger than a determined threshold, the presence of the tear is notified, otherwise the presence of a hole is notified. The voltage sent to the electrodes is an impulse voltage and has a frequency between 0 and 1500 Hz depending on the speed of the sliding of the film. Such a system counts the number of discharges in order to discriminate between punctiform holes and wider tears.

The detection of defects is particularly important in the pharmaceutical field, in which the integrity and the isolation of the content is an absolutely critical factor. It is object of the present invention a system which overcomes the drawbacks and solves the problems of the prior art.

It is sbject matter of the present invention a system for controlling defects in closed containers of non-conductive material, comprising:

A. a subsystem for dragging the containers; B. two electrodes, connected to an alternating high frequency voltage source, which are applicable on predefinable zones of said containers along a stretch of their passage;

C. a subsystem of acquisition of data relevant to the voltage signal which passes through the containers; D. a data elaboration subsystem, characterised in that the data elaboration subsystem carries out the following operations:

E. comparison of said voltage signal which passes through the containers with a threshold value SV; F. determination of the presence of defects in the case where the number of exceedings of said threshold value SV is greater than a minimal predefinable number m, the threshold SV being automatically adjusted by the data elaboration subsystem as a function of the values relevant to voltage signal acquisitions between two measurements of two subsequent samples.

Preferably according to the system, the determination of the value of the threshold value adjustment takes place according to the following steps: - acquisition of the signal for a number n of the applied alternating voltage;

- calculation of the mean square root or RMS of the acquired values; - calculation of the signal-to-noise ratio (S/R) using the preceding threshold value SV as a signal value;

- calculation of the adjustment of the threshold value SV in order to maintain the signai-to-noise ratio (S/R) around a predefined reference value. Preferably according to the system, A? ≥ 10, the number of samplings of the signal being greater or around equal to 100.

Preferably according to the system, in the first measurement said threshold value SV is a predefined threshold value, determined by taking into account possibly the last threshold value used by the system for measurements on containers of the same type.

Preferably according to the system, in the first measurement on a container, said threshold value SV is a threshold value that is predefined as a function of the dragging speed of the containers.

Preferably according to the system, in the first measurement on a container said threshold value SV is a threshold value which is predefined as a function of the thickness of the constitutive material of the containers. Preferably according to the system, in the first measurement said threshold value SV is a threshold value that is predefined as a function of the diemension of the defects to be detected. Preferably according to the system, in the first measurement said threshold value SV is a threshold value that is predefined as a function of the conductivity of the filling material of the containers.

Preferably according to the system, said threshold value SV diminishes in a non-linear way as the conductivity of the filling material of the containers increases.

Preferably according to the system, the pre-definition of said threshold value SV is made by trials and errors. Preferably according to the system, said threshold value SV is automatically adjusted by the data elaboration system even on the basis of the variation of the good phials signals with respect to said threshold value SV.

Preferably according to the system, said predefined reference value is comprised between 3 and 7.

Preferably according to the system, said predefined reference value is comprised between 4 and 6. Preferably according to the system, said predefined reference value is equal to about 5.

Preferably according to the system, said predefinable minimal number m is equal to 2.

Preferably according to the system, the electrodes, in the case of long and narrow containers, are applied on the two vertical ends.

Preferably according to the system, the electrodes, in the case of long and narrow containers having a prebreaking line, are applied along this prebreaking line.

Preferably according to the system, the alternating voltage frequency is comprised between 350 and 650 Hz.

Preferably according to the system, the frequency of the alternating voltage is comprised between 450 and 550 Hz.

Preferably according to the system, the alternating voltage is a sinusoidal voltage. The invention will be described in the following by way of illustration but not by way of limitation, with particular reference to some embodiments and making specific reference to the figures of the enclosed drawings, wherein:

- figure 1 shows a first device according to the prior art; - figure 2 shows a secondary device according to the prior art;

- figure 3 shows a third device according to the prior art;

- figure 4a shows a first portion of an outline flow diagram of the functioning of the system according to the invention; - figure 4b shows the second portion of an outline flow diagram of the functioning of the system according to the invention;

- figure 4c shows a third portion of an outline flow diagram of the functioning of the system according to the invention.

The system according to the invention comprises:

- a subsystem for the dragging of containers;

- two electrodes, connected to an alternating high frequency voltage source, which are applicable to predefinabie zones of said containers along a stretch of their passage, in particular at the ends of the container like in figure 3 that is relevant to prior art or aiong a possible pre-breaking ring of phials;

- a subsystem for the acquisition of data that are relevant to the voltage signal which passes through the containers; - a data elaboration subsystem.

The subsystem of data elaboration menages the acquisition of data and the recognition of the presence of defects such as cracks or holes, or punctiform defects or large defects.

Making reference to figures 4a to 4c, the subsystem of data elaboration initialises and controls the whole system and acquires the data useful to the measurement.

Afterwords, it activates the section of generation of the high- voltage and starts the control of the presence of the container, for example blister, in the point of the production line wherein the electric detector is installed.

If a container is present, the acquisition of the measurement signal is started. One measures the maximum of a sinusoid cycle.

The elaboration unit compares then the measured value with a predefinabie threshold value SV. Here one can choose whether there has to be an only exceeding or more exceedings. From the trials made by the applicant, one has noticed that even an only exceeding can suffice, however we to exceeding is the system achieves a remarkable efficiency. A value greater than 2 doθs not improve the efficiency very much whilst it slows down the operations.

If the threshold values is exceeded, then the container is not integral or suited to standards. It is here to be specified that the threshold value SV, as it will be explained in the following, is adjusted as a function of the carried-out measurements during the production cycle.

Instead, the first threshold value to be used at the beginning of the control cycle can be either a value of a preceding control cycle of the same container or container type, or it can be chosen besides as a function of:

- dragging speed of the containers;

- thickness of the material which constitutes the containers;

- dimension of the defects to be detected; - conductivity of the filling material of the containers (for example it reduces in a non-linear way as the conductivity of the filling material of the containers increases).

Additionally, the threshold value SV is automatically adjusted by the data elaboration system even on the basis of the variation of the signals of the good phials, in order to remedy to changed external conditions such as relative humidity (humidity closed to the electrodes or phials partially damp outside) or the level of cleaning of the containers.

Once identified the presence of a defect, the data elaboration subsystem calculates the position of the non-suited samples and an appropriate subsystem ejects them and informs about that the data elaboration subsystem.

At this point, once identified the presence of a new container, one starts again (thanks for example to photocells).

In figure 4b the steps for the control of the correct passage of the containers are illustrated, which make use of a timer and of a procedure of machines switching-off in case of fault.

As above mentioned, between the measurement in a container and the subsequent measurement on the subsequent container, one effectuates a test in order to monitor the background noise and to adapt the threshold value SV.

Making reference to figure 4c, to this end one acquires n sinusoid cycles (or in general n alternating signal cycles) and one calculates the mean square root of the samplings.

For the usual rules of statistics, confirmed in the specific case by the tests carried out by the applicant, the value of n is preferably greater than or equal to 10 and the samplings greater to or equal to 100 (the used frequency of the oscillating signal has been for example of around 500

Hz).

One is now able to calculate the signal-to-noise ratio, utilising the old threshold value as signal value.

One proceeds therefore to a variation of the threshold value SV in order to maintain constant the signal-to-noise ratio S/R, from the carried- out test a ratio equal to 5 resulting as particularly suited.

The system according to the invention allows therefore to maintain the reliability level of the defects presence detection almost constant, thanks to the feedback adjustment of the threshold value SV. This is realised in such a way to exploit the dead times between a measurement and the other, without therefore the need of slowing down the production cycle.

The system according to the invention guarantees further a minimal initial work for adapting the first threshold value to the type of containers to be analysed.

With the system according to the invention the production, for example in the pharmaceutical field, of products in isolation from the environment results of the greatest reliability, and hence the consumer is guaranteed about the integrity and the quality of the same products. The preferred embodiments have been above described and some modifications of this invention have been suggested, but it should be understood that those skilled in the art can make variations and changes, without so departing from the related scope of protection, as defined by the following claims.

Claims

1. System for controlling defects in closed containers of non- conductive material, comprising:

2. System according to claim 1 , characterised in that the determination of the value of the threshold value adjustment takes place according to the following steps:

- acquisition of the signal for a number n of the applied alternating voltage;

- calculation of the mean square root or RMS of the acquired values;

- calculation of the signal-to-noise ratio (S/R) using the preceding threshold value SV as a signal value;

- calculation of the adjustment of the threshold value SV in order to maintain the signal-to-noise ratio (S/R) around a predefined reference value.

3. System according to claim 2, characterised in that n > 10, the number of samplings of the signal being greater or around equal to 100.

4. System according to any claim 1 to 3, characterised in that in the first measurement said threshold value SV is a predefined threshold value, determined by taking into account possibly the last threshold value used by the system for measurements on containers of the same type.

5. System according to claim 4, characterised in that, in the first measurement on a container, said threshold value SV is a threshold value that is predefined as a function of the dragging speed of the containers.

6. System according to claim 4 or 5, characterised in that in the first measurement on a container said threshold value SV is a threshold value which is predefined as a function of the thickness of the constitutive material of the containers.

7. System according to any claim 4 to 6, characterised in that in the first measurement said threshold value SV is a threshold value that is predefined as a function of the diemension of the defects to be detected.

8. System according to any claim 4 to 7, characterised in that in the first measurement said threshold value SV is a threshold value that is predefined as a function of the conductivity of the filling material of the containers.

9. System according to claim 8, characterised in that said threshold value SV diminishes in a non-linear way as the conductivity of the filling material of the containers increases.

10. System according to claim 4, characterised in that the pre- definition of said threshold value SV is made by trials and errors.

11. System according to any claim 1 to 10, characterised in that said threshold value SV is automatically adjusted by the data elaboration system even on the basis of the variation of the good phials signals with respect to said threshold value SV.

12. System according to any claim 1 to 11 , characterised in that said predefined reference value is comprised between 3 and 7.

13. System according to claim 12, characterised in that said predefined reference value is comprised between 4 and 6.

14. System according to claim 13, characterised in that said predefined reference value is equal to about 5.

15. System according to any claim 1 to 14, characterised in that said predefinable minimal number m is equal to 2.

16. System according to any claim 1 to 15, characterised in that the electrodes, in the case of long and narrow containers, are applied on the two vertical ends.

17. System according to any claim 1 to 15, characterised in that the electrodes, in the case of long and narrow containers having a prebreaking line, are applied along this prebreaking line.

18. System according to any claim 1 to 17, characterised in that the alternating voltage frequency is comprised between 350 and 650 Hz.

19. System according to claim 18, characterised in that the frequency of the alternating voltage is comprised between 450 and 550

Hz.

20. System according to any claim 1 to 19, characterised in that the alternating voltage is a sinusoidal voltage.