Safety syringe abstract
A safety syringe for preventing "needle stick" injury
and/or reuse of the syringe includes a body (2), a plunger (4) mounted
within the body, connection means (24) for connecting the plunger
(4) to a needle holder (6) whereby subsequent retraction of the
plunger (4) withdraws the needle holder (6) and the needle with
a shielded position within the body (2) effected by a vacuum chamber
(18) defined between the plunger (4) and the syringe body (2), vacuum
being created within the chamber (18) by movement of the plunger
(4) during the injection stroke and serving to withdraw the plunger
(4), the needle holder (6) and needle after injection pressure is
removed. The syringe may be provided with braking means (20) to
control the rate of withdrawal of the needle and/or to prevent withdrawal
until the injection stroke of the plunger (4) has been completed.
Safety syringe claims
I claim:
1. A syringe comprising:
a body having a forward end, a rearward end, and a bore extending
from the forward end to the rearward end;
a needle holder slidably disposed within said bore proximate said
forward end;
a plunger having an end mounted slidably within said bore of said
body, said plunger extending out of said rearward end of said body;
connecting means for connecting said plunger to said needle holder
on completion of an injection stroke of said plunger by injection
pressure on said plunger so that subsequent retraction of said plunger
withdraws said needle holder and any needle mounted thereon into
a shielded position within said bore of said body;
a first sealing member on said plunger extending radially into
sliding sealing engagement with said body;
a second sealing member on said body between said first sealing
member and said rearward end of said body and extending radially
with sliding sealing engagement into said plunger; and
a chamber defined between said first and second sealing members,
so that a vacuum is created within said chamber by movement of said
plunger during the injection stroke and resultant movement of said
first and second sealing members relatively apart, and said vacuum
withdraws said plunger and said needle holder toward said rearward
end after injection pressure on said plunger is removed.
2. A syringe as claimed in claim 1 and further comprising:
a plurality of pivotable fingers within said bore proximate said
forward end of said body, said fingers being resiliently urged radially
inwardly for forming an iris substantially occluding said forward
end of said body when said needle holder is drawn into said bore.
3. A syringe as claimed in claim 1 wherein said bore has a longitudinal
axis and further comprising:
means on said needle holder inclined relative to said longitudinal
axis for inclining a needle thereon at an angle to said longitudinal
axis.
4. A syringe as claimed in claim 1 wherein said connecting means
comprises:
a protuberance at said end of said plunger within said bore; and
a complementary undercut recess in said needle holder engageable
with said protuberance.
5. A syringe as claimed in claim 4 and further comprising:
a radially extending retaining flange on said needle holder;
complementary needle holder engagement means within said bore releasably
engaging said retaining flange, and co-acting means on said plunger
and needle holder for releasing said retaining flange from said
complementary engagement means upon connection of said protuberance
with said undercut recess.
6. A syringe as claimed in claim 1 and further comprising;
stop means on said body adjacent said rearward end of said body
for arresting movement of said plunger during a preparatory forward
stroke of said plunger for preventing said connecting means from
connecting said plunger to said needle holder on completion of said
preparatory stroke; and
stop engagement means on said plunger adapted to engage said stop
means on said preparatory forward stroke and render said stop means
inoperative by a subsequent rearward stroke of said plunger so that
said stop means does not impede said plunger during the injection
stroke.
7. A syringe as claimed in claim 6 wherein;
said bore forms an inner seat on said body;
said stop means comprises an abutment removably disposed on said
inner seat; and
said stop engagement means engages said abutment during the preparatory
forward stroke so that said abutment is sheared from said body by
a rearward stroke of said plunger.
8. A syringe as claimed in claim 7 wherein said connecting means
comprises:
a protuberance at said end of said plunger within said bore; and
a complementary undercut recess in said needle holder engageable
with said protuberance.
9. A syringe as claimed in claim 8 and further comprising:
a radially extending retaining flange on said needle holder;
complementary needle holder engagement means within said bore releasably
engaging said retaining flange, and co-acting means on said plunger
and needle holder for releasing said retaining flange from said
complementary engagement means upon connection of said protuberance
with said undercut recess.
10. A syringe as claimed in claim 9 and further comprising:
a plurality of pivotable fingers within said bore proximate said
forward end of said body, said fingers being resiliently urged radially
inwardly for forming an iris substantially occluding said forward
end of said body when said needle holder is drawn into said bore.
11. A syringe as claimed in claim 10 wherein said bore has a longitudinal
axis and further comprising:
means on said needle holder inclined relative to said longitudinal
axis for inclining a needle thereon at an angle to said longitudinal
axis.
12. A syringe as claimed in claim 6 wherein said connecting means
comprises:
a protuberance at said end of said plunger within said bore; and
a complementary undercut recess in said needle holder engageable
with said protuberance.
13. A syringe as claimed in claim 1 and further comprising:
resilient braking means for retarding retraction of said plunger
disposed within a space between said bore and said plunger, said
braking means being disposed on one of said body and plunger and
in slidable engagement with the other of said body and plunger for
providing a braking force sufficient to retard but not stop retraction
of said plunger.
14. A syringe as claimed in claim 13 wherein:
said braking means further comprises braking modifying means on
said body and cooperating means on said braking means; said braking
modifying means being adapted to bear against said cooperating means
so that relative movement therebetween during the injection stroke
reduces said braking force after the injection stroke.
15. A syringe as claimed in claim 14 wherein:
said bore comprises zones having different internal diameters;
abutment means are provided on said plunger engageable with said
braking means during the injection stroke; and
said resilient braking means comprises a resilient cylindrical
member slidable on said body and having rib means resiliently bearing
against said plunger for exerting a braking force, said resilient
cylindrical member being longitudinally moveable within said zones
of different internal diameter by said abutment means for reducing
the braking force on said plunger.
16. A syringe as claimed in claim 13 wherein said connecting means
comprises:
a protuberance at said end of said plunger within said bore; and
a complementary undercut recess in said needle holder engageable
with said protuberance.
17. A syringe as claimed in claim 13 wherein said bore has a longitudinal
axis and further comprising:
means on said needle holder inclined relative to said longitudinal
axis for inclining a needle thereon at an angle to said longitudinal
axis.
Safety syringe description
FIELD OF THE INVENTION
The present invention relates to a syringe, and more particularly
to a safety syringe for preventing contamination, fear of contamination
and physical injury by "needle stick" by the syringe needle
after use and/or for preventing reuse of the syringe.
BACKGROUND OF THE INVENTION
In order to minimize the risk of contamination from a used syringe,
it is common practice for used syringes to be deposited into heavy
duty plastic bins which cannot be pierced by the needles. The bin
and contents are then moved to a disposal facility at which they
are incinerated. This means of disposal is of limited effect as
it does not eliminate "needle stick" risk between needle
use and disposal. Current disposal methods are also relatively expensive.
Numerous attempts have been made to design an acceptable syringe
in which, after use, the needle is withdrawn into the body of the
syringe and retained there in some manner. These designs are all
directed to the same end of covering the needle after use to prevent
inadvertent "needle stick" injuries with their attendant
risk of cross-infection and to prevent reuse of the syringe. In
many of these prior art arrangements the withdrawal of the needle
into the body is entirely manual and requires the syringe user to
remember to make some deliberate relative movement, normally between
the plunger and the body, to effect withdrawal of the needle into
the body of the syringe. Proposals have been made, as in Australian
Patent Specifications 593513 594634 and 35676/89 to induce
automatic withdrawal of the plunger into the body by the use of
a helically coiled spring. This necessitates the use of additional
and costly parts in the syringe and complicates its assembly.
In its first aspect the present invention is directed to an alternative
arrangement for the automatic withdrawal of a syringe needle into
the body of the syringe.
The above Prior art proposals for automatic withdrawal of the plunger
have the disadvantage that immediately upon removal of the positive
manual pressure holding the plunger in a depressed condition the
spring will immediately stop movement of the plunger to its extended
condition and simultaneously commence withdrawal of the needle into
the body of the syringe. This could cause tissue tear and inadvertent
and unwanted suction of blood into the syringe unless the operator
consciously keeps the plunger depressed until the syringe is fully
withdrawn from the patient's body. In a second aspect the present
invention provides braking means to slow at least the initial rate
of withdrawal of the needle into the body of the syringe.
BRIEF SUMMARY OF THE INVENTION
According to a first aspect of the present invention there is provided
a syringe comprising a body, a plunger mounted within the body,
means for connecting the plunger to a needle holder at the end of
an injection stroke of the plunger whereby subsequent retraction
of the plunger withdraws the needle into a shielded position within
the body, and energy storage means energizable by the insertion
stroke to cause such withdrawal of the plunger and needle after
the injection stroke. The energy storage means comprises a vacuum
chamber defined between the plunger and the syringe body, vacuum
being created within the chamber by movement of the plunger during
the injection stroke, said vacuum serving to withdraw the plunger
and needle after injection pressure is removed.
According to a second aspect of the present invention there is
provided a syringe comprising a body, a plunger mounted within the
body, means for connecting the plunger to a needle holder at the
end of an injection stroke of the plunger whereby subsequent retraction
of the plunger withdraws the needle into a shielded position within
the body, and energy storage means energizable by the insertion
stroke to cause such withdrawal of the plunger and needle after
the injection stroke, resilient braking means being disposed within
the space defined between the body and the plunger, and being disposed
on one of them and bearing against the other sufficiently to retard
but not stop the withdrawal of the plunger and needle after the
injection stroke.
In a preferred embodiment of the second aspect of the invention
the resilient braking means is formed integrally with sealing means
defining one end of the vacuum chamber of the first aspect of the
invention. It is to be understood, however, that the resilient braking
means could be applied to a syringe in which the energy storage
means is other than a vacuum chamber.
It is preferred that the resilient braking means is moveable longitudinally
of that one of the body and the plunger to which it is affixed so
as to alter the braking force it applies to the other of those members.
This allows the withdrawal of the plunger under the action of the
vacuum chamber to be prevented until the completion of injection
stroke of the plunger if desired.
In a third aspect the present invention consists in a syringe comprising
a body, a plunger mounted within the body, means for connecting
the plunger to a needle holder at the end of an injection stroke
of the plunger whereby subsequent retraction of the plunger withdraws
the needle into a shielded position within the body, stop means
attached to the body or to the plunger to prevent depression of
the plunger into the body sufficient to connect the plunger to the
needle holder in a first stroke of the plunger into the body, engagement
means on the other one of the body or the plunger to engage the
stop means upon completion of the first stroke of the plunger and
to render the stop member inoperative upon a first retraction of
the plunger to draw an injectable liquid into the syringe following
the first stroke such that the plunger may be connected to the needle
holder on completion of the following injection stroke.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be further described with reference to the
accompanying drawings wherein;
FIG. 1a is a schematic longitudinal cross-section of a syringe
in accordance with the preferred embodiment of the invention showing
the syringe in a condition prior to use;
FIG. 1b is a view similar to FIG. 1a showing the syringe in a condition
at the end of its injection stroke in engagement with the needle
holder for the syringe needle;
FIGS 2a-2e are five longitudinal cross-sectional views through
a syringe according to another embodiment of the present invention,
FIG. 2a showing the syringe in the condition in which it is shipped
for use, FIG. 2b showing the syringe in a condition ready to draw
up an injectable liquid, FIG. 2c showing the syringe in a condition
in which the liquid has been drawn up and the dose of the liquid
is about to be selected with an accompanying exclusion of air from
the syringe, FIG. 2d shows the syringe in a condition immediately
after the injection has been given, and FIG. 2e shows the syringe
in a condition after the needle has been automatically withdrawn
into the syringe body;
FIG. 3 is a longitudinal cross-sectional view through one end of
a narrow base syringe according to another embodiment of this invention;
and
FIG. 4 is a longitudinal cross-sectional view through a needle
holder and adjacent end of the body of a wide base syringe according
to another embodiment of the present invention.
DETAILED DESCRIPTION
The syringe shown in FIGS. 1a and 1b comprises a body 2 and a plunger
4 mounted within the body 2. A needle holder 6 is mounted at the
forward or inner end of the body 2 by means of an annular array
of releasable locking pawls 8 which normally engage over a shoulder
10 of the holder 6 in order to prevent retraction of the holder
6 into the body 2. A forwardly-projecting part 12 of the needle
holder 6 is of conventional form in order to mount a standard needle
which is a friction fit on the holder. Alternatively the body 2
can mount a needle with an integral holder 6b as shown in the lower
part of FIG. 1b, the holder 6b co-operating with the releasable
pawls 8 in the same manner as the holder 6. The pawls 8 extend rearwardly
from a sleeve 13 which centers the needle holder in the body 2.
The plunger 4 carries, towards its forward end, an annular travelling
seal 14 in sliding contact with the inner surface of the syringe
body 2. The seal 14 is intended to form a high quality hermetic
seal and is shaped to define a series of axially spaced annular
sealing zones against the body 2. A similar high quality annular
seal 16 is fixedly mounted on the body 2 towards its rear or outer
end. This fixed seal 16 has on its inner surface a series of annular
sealing zones which seal against the outer surface of the plunger
4. The space 18 defined between the two seals 14 16 constitutes
a vacuum chamber. Upon actuation of the syringe the movement of
the seal 14 away from the seal 16 generates a vacuum in the vacuum
chamber 18 to cause eventual withdrawal of the holder 6 or 6b together
with the needle into the syringe body 2 after use.
The forward end of the plunger 4 includes a radially-extending
braking flange 20 which frictionally engages the inner surface of
the body 2 in order to prevent non-intentional retraction of the
plunger 4 under the influence of the vacuum created in the vacuum
chamber 18. The braking flange 20 is a resilient flange defined
at an outer edge of a conical wedge 22 formed at the forward end
of the plunger. The conical wedge 22 is adapted to co-operate with
the retaining pawls 8 for the needle holder in order to release
the pawls 8 as will subsequently be described. The forward end of
the plunger is also formed with an annular array of flexible pawls
24 arranged inwardly of the conical wedge 22. The pawls 24 are shaped
to engage into an undercut groove 26 formed in the head of the needle
holder in order to anchor the needle holder to the plunger 4 when
the plunger 4 is in its forward position.
A removable stop ring 28 is mounted in an inner annular seat formed
in the inner surface of the body 2 rearwardly of the fixed seal
16. The stop ring 28 is a split ring which is resiliently biased
to an external diameter greater than that of the inner seat. An
outer seat 30 for the stop ring 28 is formed in the body 2 rearwardly
of the inner seat. The stop ring 28 has, on its internal surface,
an annular groove 32 adapted to receive an annular rim 34 formed
on the external surface of the plunger 4 towards the rear end of
the plunger.
The syringe is supplied with the plunger 4 in its retracted position.
In order to use the syringe, the plunger 4 is pushed inwardly to
expel most of the air from the fluid-receiving chamber which is
defined between the forward end of the plunger 4 and the needle
holder 6 or 6b. Insertion of the plunger during this phase is limited
by the stop ring 28 the rear edge of which engages a shoulder 36
at the outer end of the plunger 4. In this limit position, the annular
groove 32 in the stop ring 28 is axially aligned with, and is engaged
by, the projecting annular rim 34 on the plunger body whereby the
stop ring 28 is releasably connected to the plunger 4. The stop
ring 28 prevents insertion of the plunger 4 to its forwardmost position
and hence prevents connection of the pawls 24 at the forward end
of the plunger 4 with the groove 26 in the head of the needle holder.
The plunger 4 can then be retracted to draw fluid into the fluid
chamber of the syringe. It is to be noted that during this mode,
the braking flange 20 on the plunger frictionally engages the inner
wall of the body 2 in order to prevent retraction of the plunger
under the influence of the vacuum generated within the vacuum chamber
18 during the insertion of the plunger. As mentioned above, at the
end of the initial insertion stroke, the stop ring 28 is engaged
by, and is connected to, the plunger. As the plunger is withdrawn
to draw fluid into the chamber, the stop ring 28 is withdrawn with
the plunger until the stop ring 28 is clear of the inner seat. When
the stop ring moves into alignment with the outer seat 30 the inherent
resilience of the stop ring 28 enables the stop ring to expand into
the outer seat 30. The increased diameter of the outer seat 30 enables
the stop ring 28 to expand to such a diameter that it disengages
from the annular rim 34 on the plunger and is retained in the outer
seat, as shown in the lower half of FIG. 1. A retaining lip 37 at
the outer end of the outer seat 30 ensures that the ring 28 is retained
within the seat in order to prevent accidental displacement of the
ring 28 and possible jamming of the plunger.
When the required quantity of fluid has been drawn into the fluid
chamber, the plunger is then depressed in order to expel air from
the chamber in the usual manner and then to discharge the fluid
into the patient. It is to be noted that as the plunger reaches
the end of its injection stroke, the plunger is no longer subject
to the influence of the stop ring 28 which is now in its larger
diameter outer seat 30 and this enables the plunger to be moved
into its fully forwards condition for discharge of substantially
the entire contents of the fluid chamber. During the injection stroke,
vacuum again builds up in the vacuum chamber 18 the effect of this
vacuum being resisted by the braking flange 20 which frictionally
engages the inner surface of the syringe body.
As the plunger nears the end of its injection stroke, that is beyond
the stop position previously defined by the presence of the stop
ring 28 when in its inner seat, the conical wedge 22 contacts the
retaining pawls 8 in order to deflect these pawls outwardly beyond
the retaining shoulder 10 on the needle holder and into engagement
with the inner surface of the syringe body as shown in the lower
half of FIG. 1. At the same time, the pawls 24 at the plunger move
into snap-engagement in the undercut groove 26 in the head of the
needle holder in order to connect the needle holder with the plunger.
The rear ends 8a of the retaining pawls 8 constitute shear knives
which, when the pawls 8 are deflected outwardly by the wedge 22
lie against the inner surface of the syringe body in order to contact
the braking flange 20 and to deflect the flange 20 inwardly and
rearwardly by plastic deformation of the flange, thereby reducing
or removing the frictional contact between the braking flange 20
and the syringe body. When manual pressure is removed from the rear
end of the plunger and with the braking action of the braking flange
20 removed or reduced consequent on its plastic deformation, the
vacuum generated in the vacuum chamber 18 during the injection stroke
acts to withdraw the plunger and thus the needle holder and needle
which is now attached to the plunger. In the withdrawn position
of the plunger, the needle is enclosed fully within the plunger
body with no portion of the needle exposed for accidental contact.
The needle holder is a relatively loose fit on the pawls 24 so that
the axis of the needle holder and needle can incline relative to
the syringe body whereby the tip of the needle will lie to one side
of the syringe body and will be prevented by the sleeve 13 from
accidental extension from the body. The sleeve 13 may also comprise
a central iris structure held open by the needle holder when in
its operative position. As soon as the needle holder is withdrawn
by the plunger, the iris structure contracts or closes in order
to close the central aperture of the sleeve 13 and thereby to prevent
any access to the interior of the syringe body.
As no part of the needle is exposed after use of the syringe, the
syringe can be disposed of in a conventional plastic bag. The absence
of exposure of the needle also assists in preventing the spread
of infection by contaminated needles.
The syringe shown in FIGS. 2a to 2e comprises a body 100 and a
plunger 101. A needle holder 102 is mounted at the forward or inner
end of the body 100. The needle holder 102 has at its forward end
a cylindrical boss 103 inclined slightly to the longitudinal axis
of the syringe body 100. A needle 104 is disposed on the boss 103
and is held in place thereon by a conventional U-lock fitting 105.
Due to the inclination of the boss 103 the needle 104 is also inclined
to the longitudinal axis of the body 100. The needle holder 102
has a bore 106 extending longitudinally through it and communicating
at one end with an undercut recess 107 adapted to engage with a
suitably shaped protuberance on the plunger as will be hereinafter
described, and at the other end with the needle 104. A flange 108
on the needle holder 102 surrounding the undercut recess 107 engages
behind an annular rib 109 on the inside wall of the body 100. A
plurality of triangular sprags 111 project inwardly from the forward
end of the body 100 and engage about the circumference of the needle
holder 102. The engagement of the flange 108 of the needle holder
102 with the annular rib 109 of the body 100 and the engagement
of the sprags 111 about the circumference of the needle holder 102
serve to securely locate the needle holder at the forward end of
the body 100 until it is released therefrom by engagement with the
plunger as will be hereinafter described.
The body 100 defines a substantially cylindrical bore 110 extending
from the annular rib 109 which retains the needle holder 102 in
place at the forward end of the body 100 to a second annular rib
113. Rearwardly of the annular rib 113 the body 100 increases in
internal diameter through a frusto-conical zone 114 to a substantially
cylindrical zone 115. The cylindrical zone 115 is directly connected
to a second cylindrical zone 116 of slightly increased internal
diameter which in turn is connected to a tapering zone 117 which
tapers outwardly in diameter to the free end 119 of the body 100.
Between the zones 116 and 117 the body is formed integrally with
an annular collar 118. This collar 118 is molded extending rearwardly
of the junction between the zones 116 and 117 and is then turned
over to lie within zone 116 forming an inwardly directed annular
abutment. The free end- 119 of the body 100 is molded integrally
with a pair of diametrically opposed stop members 121 joined by
a thin flexible ring 122. The stop members 121 and ring 122 are
also molded integrally with, and extend rearwardly of, the body
100 and are then turned over to lie within the zone 117.
A resilient annular braking and sealing member 123 is positioned
within the zones 115 and 116 of the body 100. The member 123 includes
a pair of inwardly directed annular sealing lips 124 extending radially
inwardly from the member 123 and adapted to sealingly and slidably
engage about the plunger 101. Rearwardly of the lips are three braking
ribs 125 which could in another embodiment of the invention be
replaced by rows of bosses which may serve the same purpose. The
braking ribs are adapted to apply a braking force to the plunger
101. The radially outer surface of the member 123 carries at its
forward end a circumferential rib 126. In the initial configuration
of the syringe the member 123 is positioned with the rib 126 abutting
against the forward end of the collar 118. The collar 118 then surrounds
part of the member 123 and serves to compress the braking ribs 125
against the plunger 101.
The rearward end of the syringe body 100 is formed with a pair
of outwardly extending finger grips 112 disposed in diametric opposition
about the body 100.
The plunger 101 includes an elongate shaft 127 and at its forward
end a radially extending sealing flange 128 in sealing engagement
with the bore 110 of the body 100. At its forward free end the plunger
101 is formed with a protuberance 129 adapted to engage with the
recess 107 in the needle holder 102. The protuberance 129 and recess
107 are so dimensioned that on engagement of the protuberance 129
in the recess 107 an inwardly directed flange 131 will be pivoted
inwardly and forwardly by contact with the protuberance 129 which
will cause the flange 108 on the needle holder to be pivoted rearwardly
and inwardly to free the flange 108 from the annular rib 109 on
the bore of the body 100.
The rearward end of the plunger 101 is formed with an enlarged
head 132 which head 132 includes at its forward end a radially outwardly
extending flange 133. The enlarged head 132 on the plunger 101 is
preferably formed by heat reforming the rearward end of the plunger
after the sealing and braking member 123 has been positioned on
the stem 127 of the plunger 101.
In use the syringe is shipped in the condition depicted in FIG.
2a. The plunger 101 is in its fully retracted position and the braking
and sealing member 123 is surrounded by the collar 118 such that
the braking ribs 125 are urged firmly against the shaft 127 of the
plunger 101.
In order to draw an injectable fluid into the syringe the plunger
101 is depressed to the position shown in FIG. 2b. The plunger 101
is depressed until it is stopped by the engagement of the flange
133 on the head 132 of the plunger 101 with a pair of inwardly directed
recesses 134 in opposed faces of the stop members 121. This engagement
occurs when the protuberance 129 on the forward end of the plunger
101 is closely adjacent but not engaged with the undercut recess
107 in the needle holder 102. Subsequent retraction of the plunger
101 will draw an injectable liquid, into which the needle has been
inserted, into the body 100 of the syringe. Such retraction will
also shear the thin connection between the stop members 121 and
the body 100 of the syringe. The dose of liquid in the syringe may
then be adjusted, and air removed from the syringe, by depression
of the plunger 101. The braking force applied to the shaft 127 of
the plunger 101 is at this point sufficient to resist movement of
the plunger 101 relative to the body 100 under the influence of
the vacuum created between the braking and sealing member 123 and
the sealing flange 128 as the plunger 101 is depressed into the
body 100. Thus movement of the plunger 101 relative to the body
100 will only occur by manual application of force to the plunger
101 by the person using the syringe.
When an injection is to be given the needle is inserted into the
patient in a conventional manner. This insertion is facilitated
by the inclination of the needle 104 relative to the body 100 of
the syringe as the body 100 is disposed at a more convenient angle
to the skin of the patient, at least in the case of intravenous
injections, than would be the case if the needle 104 was in axial
alignment with the body 100 of the syringe. The plunger 101 is then
depressed to inject the liquid into the patient. At the end of the
plunger stroke the protuberance 129 will engage with the undercut
recess 107 of the needle holder 102 as the earlier removal of the
stop members 121 now allows the plunger 101 to be fully depressed.
The engagement of the protuberance 129 with the undercut recess
107 causes the flange 108 on the needle holder 102 to be drawn radially
inwardly free of the annular rib 109 in the body 100. As the protuberance
129 is entering the undercut recess 107 so the flange 133 on the
head of the plunger 101 engages the rearward end of the braking
and sealing member 123 pushing it into zone 115 of the syringe body
100 free of collar 118. The braking and sealing member 123 can expand
radially within the zone 115 so that the braking pressure on the
shaft 127 of the plunger 101 is reduced. When the syringe is withdrawn
from the patient the vacuum created between the braking and sealing
member 123 and the flange 108 will be sufficient to slowly draw
the plunger 101 back into the body 100 of the syringe. The plunger
101 will also draw the needle holder 102 now freed from engagement
with the body 100 and the needle 104 into the body. As the needle
holder 102 is drawn into the body the free ends of the triangular
sprags 111 will spring radially inwardly to form an iris precluding
egress of the needle 104 outwardly from the now open forward end
of the syringe body 100.
The vacuum pressure created in the syringe body 100 will be sufficient
to draw the needle 104 fully into the body 100 behind the iris formed
by the triangular sprags 111 and to engage radially outwardly directed
fingers 135 on the shaft 127 of the plunger 101 behind at least
the forwardmost one of sealing lips 124. Any subsequent use of the
syringe is prevented firstly by the fact that the needle 104 is
trapped within the body 101 by the sprags 111 and the inclination
of the needle 104 and secondly by the fact that any depression of
the plunger 101 will cause fingers 135 to drag the braking and sealing
member 123 into the frusto-conical zone 114 of the body where the
braking ribs 125 of the braking and sealing member 123 will be caused
to tightly bind against the shaft 127 of the plunger 101.
The arrangement of FIG. 3 shows the application of the present
invention to a narrow bore syringe which would typically be used
for giving an injection of about 1 ml of liquid to a patient. In
this case the construction and operation of the syringe is as has
been described with reference to FIGS. 2a to 2e except that the
vacuum pressure is created between the braking and sealing member
123 and an additional sealing flange 136 mounted on the shaft 127
of the plunger 101 intermediate its ends. A step 137 on the shaft
127 causes the sealing flange 136 to move downwardly of the bore
110 as the plunger is depressed creating a vacuum between the sealing
lips 124 and the flange 136. This vacuum will draw the flange 136
rearwardly when the injection has been completed and the flange
136 will carry the plunger 101 and the needle 104 rearwardly with
it.
The arrangement of FIG. 4 shows the needle holder 102 positioned
in a wide bore syringe. In this case the arrangement is as described
with reference to FIGS. 2a to 2e except that the sprags 111 do not
need to be molded so as to spring inwardly to form an iris upon
withdrawal of the needle holder into the body 100 as the inturned
flanges 137 and 138 are sufficient to prevent the needle 104 from
being re-extended from the syringe once it has been drawn into the
body 100.
The embodiments of the invention are given for the purpose of example
only and are not intended to limit the broad scope of the present
invention as defined by the claims. The needle holder 102 could
if desired be held in place in the body 100 of the syringe by a
friction fit without the need for the rib 109. Similarly the braking
ribs 125 could be replaced by other configuration of means adapted
to apply a braking effect between the plunger 101 and the syringe
body 100. |