Testing hypodermic syringes prior to automated filling

Details Testing hypodermic syringes prior to automated filling Testing hypodermic syringes prior to automated filling

1999-02-18

2001-05-08

Metjahic, Safet (Department: 2858)

Electricity: measuring and testing

For insulation fault of noncircuit elements

Where a moving sensing electrode scans a stationary element...

Reexamination Certificate

active

06229314

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to the automated filling of hypodermic syringes. More particularly this invention concerns a system for testing the syringes prior to such filling.
BACKGROUND OF THE INVENTION
A standard prefilled hypodermic syringe has a tubular body whose front end is fitted with a needle or cannula, whose rear end is blocked by a slidable plunger, and which is fitted over the needle with a protective cap. Normally such a syringe is filled from the back, that is the assembled body, needle, and cap are held in an upright position and an automated device fills the required medicament into the body, whereupon the plunger is installed.
The subassembly comprised of the body, needle, and end cap is typically made up in a high-speed machine. The needle is fitted to the front end of the body, then the cap is fitted over the needle, all as mentioned by automatic equipment at relatively high speed.
A common problem is that the needle is set so that it is not perfectly aligned with the centerline of the body. Thus when the cap is installed the needle can touch, poke into, or even poke through the cap. This clearly creates a potentially unsanitary condition in that bacteria can enter the otherwise sealed assembly through the hole in the cap created by the misaligned needle.
The standard procedure is simply to have a worker visually examine the needle assemblies before final packaging and to pick out and discard any bad subassemblies. Such a system is, clearly, labor intensive and cannot be guaranteed to catch every bad needle subassembly, especially when the needle does not project all the way through the wall of the cap or, after poking through it, has somehow withdrawn inside to leave a hole that is nearly impossible to see. Finally it is in fact desirable to reject any subassemblies where the needle is simply too close to the cap, within say 0.1 mm to 0.2 mm, as during subsequent transport and handling the needle might well come into contact with the cap wall and pierce it.
OBJECTS OF THE INVENTION
It is therefore an object of the present invention to provide an improved system for checking hypodermic-needle assemblies prior to filling.
Another object is the provision of such an improved system for checking hypodermic-needle assemblies prior to filling which overcomes the above-given disadvantages, that is which surely and positively detects any needle subassemblies where the needle has poked into or through the cap wall and even where the needle is simply too close to the inner surface of the cap.
SUMMARY OF THE INVENTION
A syringe subassembly comprised of a tubular syringe body having a front end provided with a forwardly projecting needle and fitted over the needle with a cap of a dielectric material is tested according to the invention by juxtaposing an outer electrode with the cap, juxtaposing an inner electrode with the needle, applying a high electrical voltage across the electrodes, monitoring current flow between the electrodes, and rejecting the syringe subassembly if the monitored current flow exceeds a predetermined level. The cap is normally made of a plastic and has a higher dielectric constant than the gas surrounding the subassembly in the test station, normally air.
Thus this system does not rely on the appearance of the subassembly at all, but actually tests for a breach in the cap or an inadequate spacing between the needle and the inside surface of the cap. It can test the subassemblies at a faster rate and with more accuracy than has hitherto been possible.
According to the invention the inner electrode is juxtaposed with the conductive metallic needle inside the body, since the needle usually projects backward somewhat into the space defined by the hollow body. More particularly the inner electrode is directly contacted with the needle inside the body, although the method of this invention will work if the inner electrode is merely very closely juxtaposed with the needle.
The inner electrode is an elongated pin and is formed with a longitudinally throughgoing passage. This allows this pin to be used to flush out the body by injecting a gas through the passage into the body during and/or after the test.
Normally according to the invention four or six such subassemblies are simultaneously juxtaposed with a single outer electrode and with respective inner electrodes and current flows between the inner electrodes and the outer electrode are individually monitored. Such gang testing is facilitated when the outer electrode is elongated and of U-section and the subassemblies are juxtaposed with it by being moved longitudinally along the outer electrode.
The high electrical voltage according to the invention is a direct current voltage of about 10 kV, preferable 12 kV to 14 kV.
The apparatus has according to the invention a holder for retaining the subassembly in a testing station, an outer electrode juxtaposed with the cap in the station, an inner electrode juxtaposable with the needle, a current supply for applying a high electrical voltage across the electrodes, and a monitoring system for detecting current flow between the electrodes so that if the monitored current flow exceeds a predetermined level the subassembly can be rejected. The inner electrode is a pin insertable into the syringe body and formed with a longitudinally forwardly open passage. Thus it is possible to pass a gas through the passage to flush out or sterilize the body.
For safest operation and reduced possibility of unwanted arcing the pin is mainly insulated and only has an exposed uninsulated tip. In addition so that the system can test several subassemblies at one time the outer electrode is of U-section, and separate inner electrodes with monitoring systems are used.
The outer electrode can be cup-shaped to be complementarily to the cap.
In order to prevent an electrostatic charge from being left on the needle subassembly, which charge could atomize a liquid subsequently poured into it and coat upper regions of the inner surface of the body that should remain dry, means is provided for discharging such an electrostatic charge. This means can generate an ion cloud around the subassembly. The mist can be stationary with the needle subassemblies being passed through it as they leave the testing apparatus.
Such a discharging unit includes discharge electrodes energized at about 5 kV of alternating current. These electrodes can be arrayed complementarily in a circle around the subassembly and holder. The ionizing head can be of other, for instance rectangular, square, or oval, shape. Furthermore the discharge unit can include nozzles alternating with the discharge electrodes and emitting jets of air for moving the discharge mist.


REFERENCES:
patent: 3623210 (1971-11-01), Shields
patent: 5389069 (1995-02-01), Weaver
patent: 3215289 (1989-11-01), None

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