Syringe latch

A syringe for controlling the amount of material or medical fluid in a syringe body which is expelled therefrom upon depression of a plunger in the syringe body. The syringe includes a syringe body having a chamber and a discharge end portion and an open opposite end portion, with a plunger received in the syringe body. A measuring ring having an inner thread in mesh with an outer thread on the plunger, with latch means for setting and holding the measuring ring and plunger and thus, permit an exact volume to be expelled from said chamber.

The invention generally relates to a syringe and in particular, the 
invention relates to a syringe having a plunger and barrel with a ring 
engaged on the plunger for dispensing controlled amounts of a fluid in the 
barrel. 
BACKGROUND OF THE INVENTION 
The prior art syringe is described in U.S. Pat. No. 4,153,056, issued May 
8, 1979. A related patent is U.S. Pat. No. 3,563,240, issued Feb. 17, 
1971. The prior art syringe includes a cylinder having a chamber and 
having a cannula with a core at a first end thereof, and having an open 
second end thereof, the cylinder has exterior finger flanges disposed 
adjacent the open second end, a plunger having a piston head with a ring 
seal disposed in the cylinder for sealing the chamber at a first end of 
the plunger and having a stem with four ribs in a cruciform shape fixedly 
connected to the piston head and having a thumb engaging flange fixedly 
connected to the four ribs at a second end of the plunger, each of the 
ribs having an Outer edge with a set of spaced notches forming an exterior 
thread, and a measuring ring having an interior thread in mesh with the 
exterior thread notches formed on the stem flanges for measuring and 
setting a selective volume in the chamber and bore for holding a selective 
volume of medical fluid. One problem with the prior art syringe is that it 
is sometimes difficult for operator to set the measuring ring at a 
selective angle relative to the plunger for setting an exact desired 
volume in the chamber and core. 
SUMMARY OF THE INVENTION 
According to the present invention, a syringe is provided with a cylinder 
having a chamber and a cannula with a bore at a first end thereof and 
having an open second end thereof, the cylinder having exterior finger 
flanges disposed adjacent to the open second end, a plunger having a 
piston head with a ring seal disposed in the cylinder for sealing the 
chamber at a first end of the plunger and having a stem with first and 
second and third and fourth ribs in a given cross shape fixedly connected 
to the piston head and having a thumb engaging flange fixedly connected to 
the four ribs. At a second end of the plunger, the ribs have respective 
outer edges with first, second, third and fourth sets of notches forming 
an exterior thread, and a measuring ring having an interior thread in mesh 
with the exterior thread notches formed on the ribs permitting a 
predetermined volume of fluid in the chamber to be dispensed by the 
plunger. The interior thread on the ring has a pair of detents projecting 
radially inwardly of the first, second, third and fourth sets of rib 
thread notches, each of which have minor thread diameters, wherein the 
first, second and third sets of stem flange thread notches have a uniform 
selective minor thread diameter for allowing clearances in a radial 
direction from the pair of detents, and wherein the fourth set of rib 
thread notches have a selective minor thread diameter which is larger than 
the uniform selective minor thread diameter whereby the pair of detents do 
not have any clearance in a radial direction from the pair of detents when 
adjacent thereto, so that the measuring ring is latched to the plunger 
upon disposition of the pair of detents on opposite sides of the fourth 
set of rib thread notches. 
By using the measuring ring thread detents an operator can set a desired 
volume of fluid which may be expelled from the syringe. The angle of the 
threads on the ribs and the measuring ring may be changed to permit a 
change in the volume to be expelled from the syringe for each revolution 
of the measuring ring. 
A principal object of the present invention is to provide a syringe which 
will expel predetermined accurate volume of fluid for each revolution-of 
the measuring ring. 
One object of the present invention is to avoid the difficulty for an 
operator in setting the measuring ring at a selective angle relative to 
the plunger or setting exactly a desired volume in the chamber and the 
bore for holding a selective volume of medical fluid. 
These and other objects and many of the attendant advantages of this 
invention will be readily appreciated as the same becomes better 
understood by reference to the following detailed description when 
considered in connection with the accompanying drawings in which:

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to the drawings wherein like reference characters designate 
like or corresponding parts throughout, there is illustrated in FIG. 1, a 
variable dosage syringe generally designated by reference numeral 10 which 
has an axis 11 and includes a hollow syringe body or cylinder 12 formed of 
a synthetic plastic material, or the like, and includes an elongated 
tubular cannula 14 having a tapered end portion 16 that is electively 
closed by a removable cap 18. As seen in FIG. 2, the cannula 14 has a bore 
20 formed therein which communicates with an internal chamber 22 of the 
syringe body 12. This chamber is adapted to receive a pharmaceutical 
preparation or the like which is intended to be dispensed from the chamber 
22 through the bore 20 of the cannula 14. 
The chamber 22 has a uniform diameter from one end to the other and is open 
at an end 24 thereof opposite the cannula 14. Laterally extending handles 
or finger flanges 26 are provided adjacent this end of the syringe body 12 
in a conventional manner. 
The medicament is expelled from the chamber 22 through the bore 20 by a 
plunger 28 having a stem portion or an integral body formed of a plurality 
of radially extending ribs 29, 30, 31, 33, in a cruciform array. The 
plunger 28 has a first or inner end portion 32 which includes an integral 
or snap on seal piston 34 formed thereon and adapted to be inserted 
through an open end 24 of the syringe body 12. The opposite end of the 
plunger 28 has an integral palm or thumb engaging base or flange 42 formed 
thereon in a conventional manner. 
The piston 34 includes an integral annular seal or flange 36 surrounding 
the piston 34 and having a diameter which is greater than the maximum 
diameter of the ribs 29, 30, 31, 33 of the plunger 28. As shown in FIG. 3, 
the flange 36 is connected to the piston 34 by an integral annular web 38 
which is formed in the piston 34 by an annular V-shaped notch 40, so that 
the web 38 has a reduced thickness as compared to the flange 36 and is 
flexible, to permit the flange 36 to serve as a wiping seal along the 
interior surface of the syringe body 12. 
A plunger limiting nut or ring 44 is provided on the plunger 28. The ring 
may be rotated to be properly located along the length of the plunger so 
that to permit a proper dosage of the material in the chamber to expelled 
through cannula 14. Thus by adjusting the distance of the annular ring 44 
from the finger flanges 26, more or less material from the syringe 10 can 
be expelled. 
As shown in FIG. 5, the ring 44 has an inner surface 46, which has a 
horseshoe shaped segmental rib or inner thread 48, that has an inner face 
49. The thread 48 has a first latch 50 and a second latch 52, which are 
located 180 degrees apart. The latch 50 has a first and second detent or 
projection 54,56. The latch 52 also has a third and fourth detent or 
projection 58, 60. The detents 54, 56, 58, 60 are made of a resilient 
conventional plastic material and each extends from the inner face 49 in a 
radially inward direction. The detents 54, 56, and 58, 60 respectively are 
disposed on the peripherally opposite sides of the ribs 29 and 31, in the 
latched condition as shown in FIG. 5. 
As illustrated in FIG. 2 and FIG. 6, the flanges 29, 30, 31, 33 have along 
their outer edges respective sets of axially spaced notches 62, 64, 66, 
68, which receive the inner thread 48. The three sets of notches 64, 66, 
68, of the respective fibs 31, 32, 33 have a uniform similar minor thread 
diameter and radius 67. The fourth set of notches 62 of the rib 29 has a 
minor thread diameter and radius 69 which is slightly larger than the 
uniform minor thread diameter and its radius 67. Thus, the latch 50 or 52 
can only engage the plunger 28 on the fourth set of notches 62 of the stem 
flange 29. It should be noted that the minor thread diameter and radius 
extends to the valley or root of the notch and in a typical example, the 
axial width of each of the notches 62, 64, 66, 68 is slightly larger than 
the corresponding axial width of each of the detents 54, 56, 58, 60 and 
also larger than the corresponding axial width of the inner thread 48. 
Thus, the tip portions of the detents 54, 56, or 58, 60 act to latch or 
hold the sides of one notch in the set of notches 62, adjacent to the root 
of the notch. 
In this embodiment 10, the ring 44 has an outer surface with a pair of ribs 
70,72. Ribs 70, 72 which are respectively disposed radially outwardly of 
the latches 50, 52 in order to aid the operator to line up the ring 44 
with the contacting flange 29 of the plunger 28. In an alternate 
embodiment (not shown), painted markings or raised arrows may be used in 
place of the ribs 70, 72. In another alternate embodiment (not 
illustrated), the ring 44 may have a rough finish or rippled finish in 
place of the smooth finish on its outer surface; or the ring 44 may have a 
plurality of equally angularly spaced ribs on its outer surface, in 
addition to the ribs 70, 72 which have a painted marking. 
In this embodiment ring 44 is adjustable relative to the ribs 29, 30, 31, 
33 by an angular displacement of the ring 44, and a half turn of the ring 
44 may provide a two cubic centimeters (cc) volume change or dose in the 
chamber 22, including the bore 20. In alternate embodiments, other doses 
may be accommodated by changing the pitch angle of the thread such that a 
single turn of the ring 44 can produce one cc or another pitch angle of 
the thread would produce 3 cc with a single turn of the ring 44. The 
advantage of the syringe 10 is that the operator avoids the difficulty in 
setting measuring ring 44 at a selective angle relative to the plunger 28, 
for exactly setting a desired volume in the chamber. 
It should be understood that the foregoing relates only to a limited number 
of preferred embodiments of the invention which have been by way of 
example only, and that is intended to cover all change and modifications 
of the examples of the invention herein chosen for the purposes of the 
disclosure which do not constitute departures from the spirit and scope of 
the invention.