Safety syringe abstract
A safety syringe for preventing "needle stick" injury
and/or reuse of the syringe includes a body (100), a plunger (127)
mounted within the body, a protuberance (129) on the plunger for
connecting the plunger to a needle holder (102) adapted in use to
carry a needle 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. The syringe includes a
braking device (123) disposed between the body (100) and the plunger
(127) to retard but not stop the withdrawal of the plunger and needle
after the injection stroke. The needle holder (102) includes a radially
extending flange (108) which engages with a complementary rib (109)
or groove on the syringe until the needle holder is engaged by the
protuberance (129) on the plunger. Engagement of the protuberance
with the needle holder deforms the needle holder by drawing the
flange (108) radially inwardly to disengage the flange from the
rib or groove on the syringe thereby allowing the needle holder
and any needle attached to it to be drawn into the body of the syringe.
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, said needle holder having an inner end;
a forwardly facing abutment in said bore facing said forward end;
a radially outwardly extending flange on said needle holder having
a radially inner portion and a radially outer portion, said radially
outer portion engaging said forwardly facing abutment in said bore;
a plunger reciprocally movable in said bore and having an inner
end;
sealing means for slidably supporting said plunger and for holding
fluid within said bore and comprising a sealing member mounted on
said inner end of said plunger and extending radially into sliding
sealing engagement with said bore, said plunger extending out of
said rearward end of said body; and
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;
said connecting means comprising an undercut recess in said inner
end of said needle holder, said recess being surrounded and partially
overlaid by said flange, and a protuberance on said inner end of
said plunger adapted to engage with said radially inner portion
of said flange and move said radially inner portion into said undercut
recess and to thereby distort said needle holder so that said radially
outer portion of said flange is displaced radially inwardly for
disengaging said flange from said abutment in said bore of said
body.
2. A syringe as claimed in claim 1 wherein:
a bore extends through said needle holder; and
said protuberance comprises a forwardly extending extension provided
with serrations adapted to engage within said bore in said needle
holder.
3. 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, said needle holder having an inner end;
a forwardly facing abutment in said bore facing said forward end;
a radially outwardly extending flange on said needle holder having
a radially inner portion and a radially outer portion, said radially
outer portion engaging said forwardly facing abutment in said bore;
a plunger reciprocally movable in said bore and having an inner
end;
sealing means for slidably supporting said plunger and for holding
fluid within said bore and comprising a sealing member mounted on
said inner end of said plunger and extending radially into sliding
sealing engagement with said bore, 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;
said connecting means comprising an undercut recess in said inner
end of said needle holder, said recess being surrounded and partially
overlaid by said flange, and a protuberance on said inner end of
said plunger adapted to engage with said radially inner portion
of said flange and move said radially inner portion into said undercut
recess and to thereby distort said needle holder so that said radially
outer portion of said flange is displaced radially inwardly for
disengaging said flange from said abutment in said bore of said
body;
a forwardly facing outer end on said needle holder;
an array of forwardly extending teeth on said needle holder surrounding
said outer end of said needle holder and projecting toward said
forward end of said body;
a flange on said forward end of said body extending radially inwardly
into said bore; and
an array of rearwardly extending teeth on said flange on said body
for interdigitating with said teeth on said needle holder.
4. A syringe as claimed in claim 3 wherein:
a bore extends through said needle holder; and
said protuberance comprises a forwardly extending extension provided
with serrations adapted to engage within said bore in said needle
holder.
Safety syringe description
BACKGROUND 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.
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.
Applicant's U.S. patent application Ser. No. 07/720499 filed
July 1991 now U.S. Pat. No. 5215533 is directed to a safety syringe
in which a vacuum generated by depression of the plunger causes
the plunger and a needle holder to which it has become attached
to be drawn securely back into the barrel of the syringe. The present
application is directed to a braking means to control retraction
of the plunger and the needle holder into the barrel, to stop means
to prevent premature engagement of the plunger with the needle holder,
and to connection means for connecting the plunger to the needle
holder.
BRIEF SUMMARY OF THE INVENTION
According to a first aspect of the present invention there is provided
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 adjacent 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;
energy storage means energisable by said injection stroke to cause
said retraction of said plunger and said needle holder; and
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 said plunger
and in slidable engagement with the other of said body and said
plunger for providing a braking force sufficient to retard but not
stop retraction of said plunger.
In a second aspect the present invention consists in 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 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
and terminating at a rearward end of said plunger;
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;
stop means on one of (a) said body adjacent said rearward end of
said body or (b) said plunger adjacent said rearward end of said
plunger, 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 the other of said body and said plunger
adapted to engage said stop means on said preparatory forward stroke
and render said stop means inoperative so that said stop means does
not impede said connecting means from connecting said plunger to
said needle holder during the injection stroke.
According to a third aspect of the present invention there is provided
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, said needle holder having a radially outwardly extending
flange engaged with a forwardly facing abutment in said bore of
said body;
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;
said connecting means comprising an undercut recess in a rearward
end of the needle holder which recess is surrounded by said flange,
and a protuberance on a forward end of the plunger, said protuberance
being adapted to engage with said undercut recess and to thereby
distort the needle holder so as to draw said flange radially inwardly
free from said abutment in said bore of said body.
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 shows the syringe in the condition in which it is shipped
for use; FIG. 2b shows the syringe in a condition ready to draw
up an injectable liquid; FIG. 2c shows 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;
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; and
FIGS. 5a-5e are five longitudinal cross sectional views through
a syringe according to another embodiment of the present invention;
FIG. 5a shows the syringe in the condition in which it is shipped
for use;
FIG. 5b shows the syringe in a condition ready to draw up an injectable
liquid;
FIG. 5c shows 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. 5d shows the syringe in a condition immediately after the
injection has been given; and
FIG. 5e shows the syringe in a condition after the needle holder
and needle have been automatically withdrawn into the syringe body.
BEST METHOD FOR CARRYING OUT THE INVENTION
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 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 connect 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 FIG. 1b. 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 forward 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 two 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 sliding radially
inwardly from the member 123 and adapted to sealingly 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 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 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 138 and 139 are sufficient to prevent the needle 104 from
being re-extended from the syringe once it has been drawn into the
body 100.
The syringe shown in FIGS. 5a to 5e is generally similar to that
described with reference to FIGS. 2a to 2e and comprise a syringe
body 200 and a plunger 201. A needle holder 202 is mounted at a
forward end of the syringe body 200. The needle holder 202 has a
body 206 which is generally cylindrical in shape and which has at
its forward end a tapering tubular boss 203 coaxial with the syringe
body 200. A needle (not shown) may be disposed on the boss 203 and
be held in place by friction fit with the tapering boss 203. The
needle holder 202 has a bore 204 extending through it and communicating
at its rear end with an undercut recess 205 which is adapted to
engage with a suitably shaped protuberance on the plunger 201 as
will be hereinafter described. A cylindrical flange 207 extends
coaxially with the syringe body 200 from the end of the body 206
adjacent the boss 203. This flange 207 is provided on its free edge
with teeth 208. The body 206 of the needle holder 202 is formed
at its other end with an outwardly directed annular flange 209 which
is adapted to engage behind an inwardly directed annular rib 210
on the inside surface of the syringe body 200. The body 206 of the
needle holder reduces in diameter slightly between the flange 207
and 209 at its respective ends such that adjacent the undercut recess
there is a slight clearance between the radially outer surface of
the needle holder 202 and the inside surface of the syringe body
200. The undercut recess 205 is bounded on its inner side by an
overhanging, inwardly directed annular lip 211.
The engagement of the flange 209 of the needle holder 202 behind
the annular rib 210 on the inside surface of the syringe body 200
serves to securely locate the needle holder 202 at the forward end
of the syringe body 200 until it is released therefrom by engagement
with the plunger as will be hereinafter described. The teeth 208
on the needle holder 202 interdigitate with corresponding teeth
212 on an inwardly directed flange 213 at the forward end of the
syringe body 200. This interdigitation prevents rotation of the
needle holder 202 relative to the syringe body 200 when the needle
holder 202 is secured in place in the forward end of the syringe
body 200.
The syringe body 200 defines a substantially cylindrical bore 214
extending from the annular rib 210 to a radially outwardly expanding
frusto-conical section of bore 215 and a cylindrical section 216
of expanded diameter adjacent the rear end of the syringe body 200.
A pair of finger engaging tabs 217 extend from diametrically opposed
sides of the rear end of the syringe body 200.
The plunger 201 includes an elongate shaft 218. At its forward
end it has an axially extending protuberance 219 formed with a series
of circumferential serrations 221. Behind the protuberance 219 is
a frusto-conical boss 222 coaxial with the plunger 201 and tapering
inwardly towards its forward end. Behind the boss 222 are a pair
of spaced apart annular enlargements 223 and 224 of the diameter
of the shaft 218 of the plunger 201. A cylindrical piston 225 formed
of a resilient rubber or plastics material is positioned about the
plunger 201 between the boss 222 and the enlargement 224. The piston
225 is held against axial movement relative to the plunger 201 by
the boss 222 and the enlargements 223 and 224. Rearwardly of the
enlargement the plunger 201 is formed with a pair of prongs 226
positioned on diametrically opposite sides of the plunger 201.
The rear end of the plunger 201 is formed integrally with a circular
head 227 lying in a plane normal to the axis of the shaft 218 of
the plunger 201. The head 227 is joined to the shaft 218 by four
ribs 228 spaced evenly around the circumference of the shaft 218.
A diametrically opposed pair of these ribs 228 carry legs 229. Each
leg 229 is formed with a bifurcated free end 231. Each leg 229 is
initially (as seen in FIG. 5a) joined to its corresponding rib 228
adjacent the head 227 and extends forwardly lying in the plane of
that rib which passes through the axis of the plunger 201. Each
leg 229 is spaced slightly radially outwardly of its corresponding
rib 228 and it extends slightly radially inwardly towards the axis
of the plunger 201 to an elbow 232 and then extends slightly radially
outwardly to the end 231.
An integral rear seal and braking member 233 is positioned within
the enlarged cylindrical portion 216 of the syringe body 200. This
member 233 has an annular body 234 formed of a resilient rubber
or plastics material and a bore 235 coaxial with the syringe body
200. At its rear end the annular body 234 has a radially outwardly
extending annular flange 236 bearing against the inside of the bore
216 and a radially inwardly extending wiping flange 237 which bears
against the shaft 218 of the plunger 201. Forwardly of flange 236
there is an annular recess 238 and then a further annular flange
239 and a further portion 241 of reduced external diameter. Down
the bore 235 of the annular body 234 there is forwardly of the flange
237 a plurality of annular braking ribs 242 then a plurality of
sealing ribs 243 and then, radially inside the portion 241 of reduced
external diameter, is a portion 244 of increased internal diameter
which terminates at its forward end in a rearwardly projecting annular
lip 245. There are a number of spaced apart abutments 240 disposed
about the inside surface of the syringe body 200 at the level of
the braking ribs 242. These abutments serve to urge the braking
ribs 242 firmly against the shaft 218 of the plunger 201 when the
rear seal and braking member 233 is in the position shown in FIG.
5a.
In use the syringe is initially in the condition shown in FIG.
5a. When the plunger 201 is depressed the piston 225 slides down
the bore 214 of the syringe body 200 until the bifurcated ends 231
of the legs 229 engage with the rearward free edge of the portion
216 of the syringe body 200. This engagement prevents connection
of the protuberance 219 with the bore 204 of the needle holder 202.
Pressure on the head 227 of the plunger 201 causes a deformation
of the legs 229 at their point of connection with the ribs 218 and
at their elbows 232 as is seen in FIG. 5b. The memory characteristics
of the plastic from which plunger 201 is formed is such that when
the plunger 201 is manually retracted from the position shown in
FIG. 5b to that shown in FIG. 5c the legs 229 spring outwardly so
that upon the plunger 201 again being depressed the bifurcated ends
of the legs will no longer contact the free end of the syringe body
200 and the plunger will be able to be fully depressed into syringe
body 200 as is shown in FIG. 5d.
The initial retraction of the plunger 201 must be done manually,
not withstanding the creation of a vacuum between the piston 225
and the rear seal and braking member 233 due to the engagement
of braking ribs 242 against the shaft 218 of the plunger 201. This
manual retraction, from the position shown in FIG. 5b to that shown
in FIG. 5c, is used to draw a liquid to be injected into the syringe
body. After adjustment of the volume of the liquid in the syringe
in the usual way the needle (not shown) is inserted into the patient
and the plunger 201 depressed.
As the injection stroke of the plunger 201 is completed the plunger
moves into the position shown in FIG. 5d. The protuberance 219 enters
the bore 204 of the needle holder and the annular ribs 221 thereon
frictionally engage with the needle holder 202. At the same time
the frusto-conical boss 222 engages with the inwardly directed flange
211 cantilevering it forwardly and radially outwardly into the undercut
recess 205 this draws the flange 209 radially inwardly. This effect
is further enhanced by the frusto-conical shape of the boss 222
which acts as a wedge to further force flange 211 radially outwardly.
As the protuberance 219 is engaging with the needle holder 202
the ribs 228 at the head end of the plunger 201 are engaging with
the rear end of the rear seal and braking member 233 and forcing
it forwardly along the cylindrical section 216 of the syringe body
200. The portion 241 of the member 233 will engage with the frusto-conical
section 215 of the syringe body 200 and be compressed radially inwardly
by it forcing the lip 245 radially inwardly towards the shaft 218.
As the rear seal and braking member is forced forwardly it slides
off the abutments 240. This allows the braking ribs 242 to expand
radially outwardly thereby reducing the braking force applied to
the shaft 218. The reduction of the braking force exerted by the
braking ribs 242 means that the vacuum generated between the rear
seal and braking member 233 and the piston 225 is sufficient to
now withdraw the plunger into the syringe body when the user's injection
pressure is removed from the head 227 of the plunger 201.
The vacuum force withdrawing the plunger 201 also withdraws the
needle holder 202 as the protuberance 219 on the plunger 201 is
engaged with the bore 204 of the needle holder 202 and the flange
209 has been drawn radially inwardly sufficiently to clear the rib
210 with which flange 209 would normally be engaged. When the plunger
202 is fully retracted by the vacuum force the prongs 226 engage
behind the radially inwardly directed flange 245 on the rear seal
and braking member 233. This engagement prevents the plunger 201
from again being depressed and traps a needle disposed on the needle
holder within the syringe body 200.
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. |