Abstrict The invention provides a disposable syringe which can be used once
only. The syringe comprises a shaft having a shaped appendix to
which a plunger slidable within the syringe cylinder is sealingly
connected. At that end at which the hypodermic needle is mounted
the cylinder comprises a hole into which a hollow element having
a shaped element integral therewith and projecting into the cylinder
is inserted and locked. This shaped element becomes securely coupled
to a portion shaped complementary to it provided at the adjacent
free end of the plunger carried by the shaft to prevent the re-use
of the syringe after the shaft has been lowered to firmly engage
the shaped portion with the shaped element projecting from the cylinder
since withdrawal of the shaft would cause disengagement of the plunger
from the shaped appendix of the shaft.
Claims I claim:
1. A disposable syringe for once-only use, comprising:
a hollow cylinder having a base wall traversed by a hole wherein
a hypodermic needle is positioned; and
a syringe operating shaft movably housed within the cylinder and
carrying a movable plunger which is releasably connected to a shaped
appendix of said shaft;
wherein said hypodermic needle is inserted and locked in said hole
in the cylinder base wall, said hypodermic needle comprising a shaped
element which projects from said hypodermic needle towards the cylinder
interior, said shaped element being securely engageable with a shaped
portion which is provided in a facing surface of said movable plunger,
said shaped portion being complementary with said shaped element;
and
an engagement force between the shaped element of said hypodermic
needle and the shaped portion in the facing surface of said movable
plunger is greater than an engagement force between the shaped appendix
of said syringe operating shaft and the movable plunger, such that
when said shaft is withdrawn in a direction away from said hypodermic
needle, the connection between said shaft and said movable plunger
will be released and said movable plunger will remain engaged with
said shaped element of said hypodermic needle.
2. A disposable syringe for once-only use, comprising:
a hollow cylinder having a base wall transversed by a hole wherein
a hollow means is positioned; and
a syringe operating shaft movably housed within the cylinder and
carrying a movable plunger which is releasably connected to a shaped
appendix of said shaft;
wherein said hollow means is inserted and locked in said hole in
the cylinder base wall, said hollow means comprising a shaped element
which projects from said hollow means towards the cylinder interior,
said shaped element being securely engageable with a shaped portion
which is provided in a facing surface of said movable plunger, said
shaped portion being complementary with said shaped element; and
an engagement force between the shaped element of said hollow means
and the shaped portion in the facing surface of said movable plunger
is greater than an engagement force between the shaped appendix
of said syringe operating shaft and the movable plunger, such that
when said shaft is withdrawn in a direction away from said hollow
means, the connection between said shaft and said movable plunger
will be released and said movable plunger will remain engaged with
said shaped element of said hollow means.
Description BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a disposable syringe, and more particularly
to a syringe which can be used only once, to prevent its re-use
particularly by drug addicts.
2. Description of the Related Art
The problem of constructing syringes which can be used only once
is very urgent, as is demonstrated by the large member of patents
offering different solutions to this problem.
British patent GB-A-2015883 and PCT patent WO 88/10127 describe
syringes comprising a plunger fixed only weakly to its shaft and
movable within the syringe cylinder, which comprises appendices
projecting inwards from the cylinder. These projecting appendices
are positioned close to the bottom of the cylinder where the syringe
needle is mounted. In this manner, when the plunger is pushed to
the bottom of the cylinder the projecting appendices engage the
plunger and cause it to separate from the shaft when the shaft is
pulled backwards away from the bottom of the cylinder. The drawback
of this type of syringe is that it is not possible in practice to
make the appendices projecting into the syringe cylinder of sufficient
size to ensure reliable engagement of the plunger.
European patent EP-A-00229017 describes a syringe comprising a
plunger with a shaped head engaged by a plurality of flexible deformable
fingers projecting from the adjacent end of the shaft. When the
syringe is used for the first time, on withdrawing the shaft it
pulls the plunger back to draw the liquid to be injected into the
syringe. Then when the shaft is pushed down the shaped head of the
plunger deforms or breaks the flexible fingers engaged with it,
after which the fingers can no longer grip the plunger to pull it
away from the bottom of the syringe and allow new liquid to be drawn
in.
The drawback of this syringe is that its structure is very complicated
and of dubious operation because it is unclear how the plunger can
be initially pushed to the bottom of the syringe cylinder without
breaking the flexible fingers of the shaft, before the syringe is
used for the first time to draw in the liquid.
U.S. Pat. Nos. 3667657 3951146 and 3998224 comprise cutting
blades or points which cut or perforate the plunger when this is
pressed to the bottom of the cylinder of the respective syringe.
Patent GB-A-2205750 describes a syringe with a plunger transversed
by holes below which a flexible membrane is provided to close the
holes when pressing the syringe shaft, but which rises from the
holes when the shaft is withdrawn from the cylinder, so preventing
liquid being drawn into the syringe.
The plunger holes and the relative membrane act as automatic unidirectional
valves.
U.S. Pat. Nos. 3934586 and 4367738 and patent GB-A-2117249
describe syringes in which the cylinders and plungers are shaped
with projecting retention teeth and respective seats shaped to allow
the shaft to move only in the direction for expelling the liquid,
which has to be present in the syringe before it is used, and to
prevent the shaft moving in the direction away from the syringe
bottom.
SUMMARY OF THE INVENTION
The main object of the present invention is to provide a disposable
syringe, i.e. usable only once, which is of simple structure, convenient
construction and reliable operation.
These and further objects are attained by a syringe comprising
a hollow cylinder with a base wall traversed by a hole at which
a hypodermic needle is or can be applied, and a syringe opening
shaft movably housed within the cylinder and carrying a plunger
releasably connected to a shaped appendix of the shaft, characterised
in that in said hole in the cylinder base wall there is inserted
and locked a hollow element from which there projects towards the
cylinder interior a shaped element securely engageable with a shaped
portion complementary to it, provided in the facing surface of the
plunger.
BRIEF DESCRIPTION OF THE DRAWINGS
The structure and characteristics of the disposable syringe according
to the present invention will be more apparent from the description
of some embodiments thereof given hereinafter by way of non-limiting
example with reference to the accompanying drawings, in which:
FIGS. 1 and 2 are a schematic axial section through a first embodiment
of a syringe, shown before and after use respectively;
FIG. 3 is a perspective view to an enlarged scale of the element
fixed to the bottom of the syringe of FIGS. 1 and 2 and provided
with a shaped appendix;
FIG. 4 is an axial section through the bottom portion of a different
embodiment of the syringe cylinder, with the element provided with
the shaped appendix fixed to it;
FIGS. 5 and 6 are schematic partial axial sections showing a further
embodiment of the syringe;
FIGS. 7 and 8 are axial sections through a further embodiment of
the syringe, showing the plunger free to slide within the syringe
cylinder, and in its locked position on the base of the cylinder
respectively; and
FIGS. 9 and 10 similar to FIGS. 1 and 2 show a syringe in which
the shaft is locked on the base of the syringe cylinder after being
pushed to the bottom of it.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Reference will firstly be made to FIGS. 1 to 3 which show a syringe
comprising a hollow cylinder 1 slidingly housing a seal element
represented by a plunger 2 constructed of elastomer material, which
is fixed by a weak joint to the lower end of an elongate shaft 3.
This weak joint is in the form of a small seat 4 provided in the
upper part (with respect to FIGS. 2 and 2) of the plunger, into
which there is press-fitted a small shaped appendix 5 projecting
from below the shaft (FIG. 1). Under these conditions, when the
appendix 5 is housed in the seat 4 of the plunger 2 movement of
the shaft relative to the cylinder 1 causes the plunger to move
within the cylinder.
In the lower part or base of the cylinder 1 there is provided a
passageway into which the upper end (with respect to the figures)
of a shaped element 6 is forced from the outside to assume a sealed
state, and remains securely fixed to the cylinder either because
it snap-fits into it (as shown in the figures) or by friction between
two opposing conical surfaces provided in the passageway and on
the outer surface of the element 6 or because the element 6 is
thermowelded or glued to the cylinder 1. The shaped element 6 is
trasversed by a channel which opens at the hypodermic needle 7 (which
can either be embedded in the element 6 as shown in the figures,
or be pressed over an outer lower conical surface of the element),
the upper end of said channel opening into a funnel-shaped recess
from which there extend ribs 8 (these being three in number in the
case illustrated), from which there projects an elongate appendix
9 the free end of which comprises a widened hook-shaped head 10.
In the plunger 2 there is provided a lowerly (with respect to the
figures) open profiled seat 11 into which the head 10 of the appendix
9 can penetrate and remain when the plunger is pushed to the bottom
of the syringe by means of the shaft 3.
Initially, before using the syringe, the shaft is in a lowered
position with the plunger 2 close to or in light contact with the
head 10 of the appendix, but in any event with the head 10 outside
the seat 11 in the plunger.
Starting from this initial rest position, after removing the protection
cap 12 for the needle 7 (in the illustrated embodiment the cap has
sat its open end a hook-shaped projecting edge which is initially
in contact with the lower conical surface of the element 6 where
it is retained by friction only, as shown in FIG. 1), the plunger
is raised from the bottom of the syringe by pulling the shaft 3.
It should be noted that during this movement, liquid is drawn into
the syringe through the needle 7 without the plunger separating
from the shaft because the joint formed by the seat 4 and the appendix
5 inserted into it ensures a sufficiently strong connection to prevent
separation of the plunger for the shaft while the liquid is being
drawn into the syringe.
When the syringe has been loaded, i.e. filled with liquid, the
liquid can be injected in the conventional manner by pressing the
plunger with a finger so that the plunger is lowered to the base
of the cylinder.
When the plunger 2 comes into contact with the head 10 of the appendix
9 further pressing of the shaft results in insertion of the head
10 into the seat 11 (the plunger deforms elastically, being constructed
of a yieldable material) until the head 10 is housed (FIG. 2) in
an inner widened part of the seat 11.
In this manner the head 10 is securely held in the seat 11 as
is immediately apparent.
At this point, if the shaft is pulled the shaft separates from
the plunger because the force with which the head 10 is held in
the plunger is greater than the force with which the appendix 5
is held in the plunger. This is easily achieved, for example by
simply making the head 10 larger than the appendix 5. This separation
of the plunger from the shaft makes the syringe unusable, and it
can therefore be used only once.
After making the injection, the cap 12 is placed over the needle
7 and forced down so that its projecting edge 13 snaps securely
(FIG. 2) into a groove 14 provided in the outer surface of the element
6 so safely protecting the needle.
FIG. 4 shows a simplified embodiment in which the plunger and shaft
(these not being shown for simplicity) are of identical structure
to those of FIGS. 1 and 2 or FIGS. 5 and 6 whereas the shaped element
to engage the plunger consists of a needle 15 fixed or welded into
an aperture provided in the base of the cylinder 16 of a syringe,
the upper end 17 of the needle projecting into the cylinder and
having at its upper free end a widened head 18 (identical to the
aforedescribed head 10) intended to penetrate and fix into the corresponding
seat of the syringe plunger.
The cavity in the needle can extend through the entire head 18
of the needle 15 in which one or more holes can also be provided
in the immediate vicinity of the base of the cylinder 16. The liquid
pushed by the plunger can thus pass through the holes 19 (if provided)
or through the cavity in the head 18 or through both if the holes
19 and the cavity in the head 18 are both provided.
In the embodiment described with reference to FIG. 4 it can be
seen that the needle 15 has the same purpose as the element 6 from
which the appendix projects, its hook-shaped portion being in this
case the head 16 of the needle itself.
With reference to FIGS. 5 and 6 these represent an embodiment
similar to that of FIGS. 1 to 3. They show, fixed to the cylinder
20 a shaped element 21 (of which for simplicity only the upper
part is shown) from which there extends an appendix (much longer
than the already described appendix 9) with a widened head 23 of
hook shape, similar to the head 10.
The seal element, represented by a plunger 24 lowerly comprises
a long seat 25 shaped in the manner of successive steps, as can
be clearly seen in the drawing.
In contrast to the embodiment shown in FIGS. 1 and 2 in which the
plunger 2 is securely hooked by the head 10 of the appendix 9 only
when the plunger is pushed practically to the bottom of the syringe,
in the embodiment of FIGS. 5 and 6 the plunger 24 is hooked by the
head 23 while the plunger is still a long way from the bottom of
the syringe, as can be clearly seen in FIG. 5. Already at this point,
if an attempt is made to pull the plunger upwards, it disengages
from the shaft, this being particularly useful if the syringe is
used by drug addicts.
In FIG. 5 the plunger 24 is shown still coupled to the shaft, whereas
in FIG. 6 the plunger is shown pushed to the bottom of the syringe
and with the shaft pulled upwards and disengaged from the plunger.
With reference to FIGS. 7 and 8 these show a portion of a syringe
in which the cylinder 26 comprises in its base a passageway defined
internally by a conical surface into which a shaped element 27 with
an at least partly conical surface is forced and securely retained.
The element 27 is fixed into said passageway by inserting it from
the inside of the cylinder and then pushing it towards the base
of the cylinder until the desired secure fit has been obtained.
As can be seen from FIGS. 7 and 8 the element 27 is internally
hollow and from that end which lies within the cylinder 26 there
project elongate flexible appendices 28 (four in number in the embodiment
shown on the drawings) with their free end 29 hook shaped.
In the lower part of the seal element plunger 30 there is provided
a profiled annular seat 31 with an enlarged part 32 in its interior.
When the plunger 30 is pushed downwards in the cylinder (from the
position of FIG. 7 to the position of FIG. 8) the appendices 28
penetrate into the annular seat 31 in the plunger until the free
ends 29 of the appendices penetrate into the enlarged parts 32 of
the annular seat, so securely hooking the plunger 30 which disengages
from the shaft (FIG. 8) when the shaft is pulled in the direction
of withdrawing of the plunger from the base of the cylinder.
Finally, FIGS. 9 and 10 show a syringe comprising a cylinder 31
in the base wall of which there is mounted a hypodermic needle 32
of which the opposite end to that comprising the needle point projects
into the cylinder and has a widened head (similar to that shown
in FIG. 4), which forms the shaped fixing element of the syringe.
In proximity to its free end within the cylinder, the syringe operating
shaft 34 comprises annular recesses or grooves, each of which houses
an annular seal such as an O-ring 35. The free end of the shaft
within the cylinder 31 comprises a recess 36 shaped in a manner
complementary to the needle head 33. In this manner, when the shaft
is pushed to the bottom of the cylinder, the needle head 33 penetrates
into the shaped recess 36 provided in the shaft, to become securely
fastened within it as shown in FIG. 10.
It can be seen that if the needle 32 is securely fixed to the cylinder
31 the shaft cannot be withdrawn for drawing new liquid into the
cylinder after it has been brought into the position (FIG. 10) in
which it is fastened onto the needle. If the needle 32 is not fixed
securely to the base wall of the cylinder, the needle is withdrawn
from the base wall to finish within the cylinder itself if the shaft
34 is pulled with sufficiently high force after fastening onto the
needle head 33 (FIG. 10) following the initial operation of the
syringe.
Only some possible embodiments of the syringe according to the
present invention are shown on the drawings, but it is apparent
that the structure of the element carrying the hook-shaped appendices
for fastening to the plunger can be easily formed in different but
equivalent ways.
In every case it can be seen that the syringe can be used only
once, and that it can be produced very easily and at low cost.
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