CA1195895A

CA1195895A - Hypodermic syringe cartridge with non-retractable drive piston

Info

Publication number: CA1195895A
Application number: CA000423996A
Authority: CA
Inventors: Ida M. Butterfield
Original assignee: BUTTERFIELD GROUP
Current assignee: BUTTERFIELD GROUP
Priority date: 1982-03-31
Filing date: 1983-03-18
Publication date: 1985-10-29
Also published as: GB2117249B; GB8308493D0; GB2117249A; JPS58173562A

Abstract

HYPODERMIC SYRINGE CARTRIDGE
WITH NON-RETRACTABLE DRIVE PISTON
ABSTRACT OF THE DISCLOSURE
The drive piston of a hypodermic syringe is rendered non-retractable by including on it a resilient disc-like element whose free diameter is slightly larger than the diameter of the glass tubular body of the syringe. The drive piston is inserted into the glass tubular body from the rear end, thereby causing the resilient disc-like element to become dished with its, concave side facing rearward. The dished resilient element acts as a continuous pawl since any attempt to retract the drive piston jams the edge of the resilient element against the inside wall of the tubular body.

Description

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1 APPLICA~ION FOR PATENT

IDA M. BUTTERFIELD

FOR

9~YPODERMIC SYRINGE CARTRID OE

1~BACKGRO~ND OF T~E l~v~lION

14 Field of the Invention The present invention is in the field of medical 16 equipmentg and more specifically relates to a cartridge 17 or a hypodermic syringe J the cartridge having a drive 18 piston that can be moved only in one direction.

20 The Prior Art 21 Vnless 1uid mediciments are to be mixed in 22 the syringe, there is no xeason why the drivç piston 23 should be retractable~ That is, since ~luid is only 24 removed from the syringe it is necessary only tha~ the 25 drLve piston be advanceable, but there is no need for 26 th~ drive piston to be retractable.
27 Cartridges for syringes known in the prior 28 art include a tubular glass member within which a drive 29 /~/

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1 piston of soft rubber slides in sealing eng~gementO

2 Motion is transmitted by khe user to the drive piston

3 by means of an actuator rod which is removably attached

4 to a metal screw that is embedded in the rubber drive

5 piston and that extends from the back side of the rubbex

6 drive piston. It is generally desirable that the resistance of the drive pis~on to advancement be sub-8 5tantially constant as opposed to intermittent.
9 The use of a pawl in devices other than hypo-10 dermic syringes to prevent mo~ion in one direction while 11 permitting motion in the oppo~i~e direction is well 12 known. However, the problems attendan~ to adapting a 13 pawl for use in a hypodermic syringe seem to be insur-14 mountable because a pawl must be associated with a toothed 15 surface, and such a surface would seem to have no place 16 inside the tubular member of the cartridge.
17 The prin~iple of a con~inuous ratchet can be 18 demonstxated by the use of a pencil having an eraser on 19 one end. The eraser of the pencil should touch the top 20 of the d~s~ and the shaft of the pencil should be inclined 21 to the desk at an angle of approximately 60 or greater.
22 It will then be found difficult to push the eraser across 23 the desk, but easy to draw the eraser in the direction 24 indicat~d by the point of the pencilO This principle is 25 applied in a well-known type of doorstop, but it was by 26 no~means apparent how this physical principle could be 27 put to use in the cartridge of a hypodermic syringe.

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su~uAaY OF THE l~vh~llON
The present inventor has succeeded in applyin~ the above-described physical principle of a continuous ratchet to produce a drive piston that can be moved in only one direction wi~hin the tubular member of the cartridge of a hypodermic syringe. This is accomplished by affi~ing to the drive piston a re6ilient member that has a diameter slightly ~reater than the diametar of the bore of the tubular member, so that when the drive piston is inserted into the tubular member, the element is forced to assume a dished shape, which i9 convex in the direction of intended motion.
The present inventor recognized that the holding power of such a dished element could conceivably be overpowered by brute force, or~ alternatively, R
lubricant could be applied to the inside wall of the tubular member to reduce the holding power of the element. These potential problems were overcome by combining the dished element with an actuator rod that is not attached to the drive piston and that therefore can push the drive piston but cannot retract it.
Thus the present invention provides an insert, psrt of which is permanently embedded within a drive piston that is pushed by an actuQting rod within a tubular ~ember of a hypodermic syrin~e to sxpel fluid from the hypoder~ic syringe, characterized in that said insert simultaneously serves the dual purposes of preventin~ retraction of the drive piston from any position alon~ the tubular member to which the drive piston has been advanced and of preventing penetration of the drive piston by a hypodermic needle, thereby rendering the hypode~mic syrin~e pilfer-proof, said insert comprisin~:
n resilient element spnnnin~ the bore of the tubular member when inside the tubular member, impenetrable by a hypodermic needle, and extendin~
radially when removed from the tubular member to a diameter greater than the bore of the tubular member so that peripheral portions of said resilient element are forced to bow rearward when the drive piston i9 inserted into the tubular member from the rear;
sQid peripheral portions frictionally contactin~ the inside wall of the tubular member, the friction between said peripher~l portions and the inside wall resistin~ rearward motion of the drive piston at all positions of the drive piston within the tubular member so that any attempt to pull the drive ~ .~
~ 3 -pigton to~ard the rear of the tubular member will force said peripheral portions to jam even more tightly against the inside wall of the tubular member, thereby preventing retraction of the drive piston at all positions of the drive piston within the tubular member.
In another aspect, the above insert may serve the additional purpose of positioning the tip of the actuating rod at the center of the drive p;ston.
This is accomplished by providing on the insert, a shank portion extending rearward beyond the drive piston and c~ntered on the axis of the drive piston.
The novel features which are believed to be characteristic of the invention, both as to organization and method of operation, together with further objects and advantages thereof, will be better understood from the following description considered in connection with - 3a -~:`

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~L~95~5 1 the accompanying drawings in which several embodiments 2 of the invention are illustrated by way of example. I~
3 is to be expressly understood, however, that the drawings 4 are for the purpose of illustration and description 5 only and are not intended as a defini~ion of the limits 6 of the invention, BRIEF DESCRIPTION OF THE DRAWINGS

12 Figure 1 is a fractional cross sectional view 13 of a first preferred embodiment of ~he hypodermic syringe 1~ cartridge of the present invention:
Figure 2 i5 a ractional cross-sectional view 16 of a second preferred embodiment o the cartridge in 17 accordance with the present invention; and 18 Figure 3 is a fractional cross-sectional view 19 o~ a third preferred embodimen~ o~ the cartridge of the 20 present invention~

2~
24 DE :eAILED DESCRIPTION OF THE PREFERRED EMBODIMEN'rS

26 ~ Figure 1 shows a first preferred embodiment 27 of the invention in which a drive piston 16 forms a .

slidable seal within the tubular member 12 so that as 2 the drive piston 15 is advanced to the left in Figuxe 1, 3 some of the fluid 14 will be expelled from the hypo-4 dermic syringe. The drive pis~on 16 di~fers from drive 5 pistons known in the prior art by the presence o~ an 6 integral disc 20 whose central portion joins the rem~;n~r

7 of the drive piston 16. In the preferred embodiment, the

8 disc 20 is composed of the same material as the resilient

9 portion o~ the drive piston 16, preferably a soft rubber.

10 The diameter of the disc 20 is slightly Iarger than the

11 diameter of the bore of the tubular member 12 so that

12 the disc 20 is forced into a dish-like shape that is

13 convex ~oward the leading end 17 of the drive piston,

14 i.e., in the direc~ion of the in~ended motion.
The drive piston 16 includes an insert 18 which 16 is useful for distributing the force applied by the actuator 17 rod 22. ~he actuator rod 22 is not normally a part of the 1~ cartridge and includes a threaded hole at its front end, 19 whieh normally engages a threaded shank of an insert of a 20 type known in the prior art. Unlike the prior art insert, 21 the insert of the pxesent invention has an unthreaded 22 shank 24 small enough in diameter to pass freely into the 23 threaded hole 26 in the actuator rod 22. The insert 18 24 also includes a circular flange 23 against which the end 25 of the actuator rod 22 bears. The ogival shape of the 26 unthreaded shank 24 deters tampering because it is 27 difficult to grip.
28 In operation, the actuator rod is slipped over 29 the unthreaded shank 24 by the user and is pushed to the 31 ~/
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:3L~5 l left in Figure l thereby forcing the drive piston 16 2 to move towards the left. ~he disc 20 produces a smooth 3 drag force of relatively small magnitude as the drive 4 piston 16 moves to the left. Because the threaded 5 hole 26 in the ac~uator rod 22 slips loosely over the 6 unthxeaded shank 24 of the insert 18, the actuator 7 rod 22 will disengage from the insert 18 when the 8 actuator rod is pulled to the right in F.igure l. If an ~ attempt is made to defeat ~his fea~ure by pu~ting a 10 sticky material in the threaded hole 26, it will be 11 found that the disc 20 ~ams agains~ the in~ide walls of 12 the tubular member 12 and thus produces a substantial 13 force opposing motion of the drive piston 16 to the right 14 in Figure 1. This force is sufficien~ly great that it l~ causes the sticky material introduced into the threaded 16 hole 26 to yield, thereby releasing the actuator rod 22.
l~ The unthreaded shank 24 serves to center and to steady 18 the actuator rod in normal usage, 1~ Figure 2 shows a second preerxed embodiment 20 o the present invention in which the insert 30 includes 21 a disc 32 that not only serves the same purpose as the 22 disc 20 of Figuxe 1, but which also ~orms an impenetable 23 barrier ~o prevent penetration of the drive piston 34 by 24 a hypodermic needle for the purpose of pilfering the 25 fluid 14 in the cartridge. In the second preferred 26 em~odiment shown in Figure 2, the disc 32 is an integral 27 part of the insert 30 and pre~erably is made of a resilient -1 metal. ~he resilient portion of the drive piston 34 is Z substantially the same as a drive piston used in the 3 prior art.
4 In opera~ion, when an attempt is made to pull 6 the drive piston 34 of Figure 2 to the right, the disc 32 6 jams against the inside wall of the ~ubular member 12 7 thereby strongly resisting any further motion of the 8 drive piston toward the right.
9 Figure 3 shows a ~hird preferred embodiment of 10 the invention which is similar to that of Figure 2, but 11 in which the inside surface of the ~ubular membex 12 12 includes a number of longit~l~;nAlly-spaced xatchet teeth 13 of which the teeth 38 are typical.
14 As the drive piston 34 i5 moved to the left,

15 the disc~like element 36 flex s to permit the motion.

16 However, if an attempt is made to move the drive piston 34 1~ to the right, the dis ~like element 36 will engage one 18 ~ the faces 40 of the ratchet teeth 38 thereby preven~ing 19 motion of the dri~e piston to the right.
The embodiment of Figure 3 ha~ a more positive 2~ ratchet action than the embodiments of Figures 1 and 2, 22 but it is believed that such a strong ratchet action is 2~ not required unless the actuator rod 22 is attached to 24 the insert 30. It is ~elieved that the embodiment of 25 Figure 3 would be more difficult to manuacture than the 26 em~odiments of Figures 1 and 2, and ~o that exten~, the 27 em~odiment of Figure 3 would be less prefexred. The 29 ~//

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1 embodiment of Figure 3, like the embodiment of Figure 2, 2 does provide an impenetrable disc to prevent pileraye 3 of the fluid 14 by inser~ion of a hypodermic needle 4 through the drive piston 34.
It is recognized that th~ element described as 6 a disc 20 of Figure 1 could be replaced by one or more finger-like projections; similax considerations apply to the disc 32 of Figure 2 and the disc-like element 36 of 9 Figure 3. The use of a disc, as opposed to fingers, is 10 preferable or preventing pilferage, as discussed above.
11 The disc-like elements 20 o~ Figure 1, 32 of 12 Figure 2 and 36 of Figure 3 could probably be over 13 powered by the application of brute force pushins the 14 piston to the right in all of the figures, but this is 15 prevented by use o~ the unthreated shank 24 which prevents 16 ~he actuator rod from being attached to the insert.

17 When the drive piston 34 o~ the embodiment of

18 Figure 3 is moved to the left, the user can feel varying

19 degrees of resistance, and this may be helpul to the

20 user as an indicator o the amount of fluid injected.

21 ~hus/ there has been described a caxtridge for 2~ a hypodermic syringe, which cartridge has a drive piston 23 that can be moved only in one direction. Several embodi-24 ments and variations o~ the invention have been disclosed, and it i5 to be understood that additional embodiments and 26 vaiations will be obvîous to those skilled in the art.
27 The embodiments described herein together with those 28 additional variations are consldered to be within the 29 scope of the invention.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY OR PRIVILEGE
IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An insert, part of which is permanently embedded within a drive piston that is pushed by an actuating rod within a tubular member of a hypodermic syringe to expel fluid from the hypodermic syringe, characterized in that said insert simultaneously serves the dual purposes of preventing retraction of the drive piston from any position along the tubular member to which the drive piston has been advanced and of preventing penetration of the drive piston by a hypodermic needle, thereby rendering the hypodermic syringe pilfer-proof, said insert comprising:
a resilient element spanning the bore of the tubular member when inside the tubular member, impenetrable by a hypodermic needle, and extending radially when removed from the tubular member to a diameter greater than the bore of the tubular member so that peripheral portions of said resilient element are forced to bow rearward when the drive piston is inserted into the tubular member from the rear;
said peripheral portions frictionally contacting the inside wall of the tubular member, the friction between said peripheral portions and the inside wall resisting rearward motion of the drive piston at all positions of the drive piston within the tubular member so that any attempt to pull the drive piston toward the rear of the tubular member will force said peripheral portions to jam even more tightly against the inside wall of the tubular member, thereby preventing retraction of the drive piston at all positions of the drive piston within the tubular member.

2. The insert of Claim 1 serving the additional purpose of positioning the tip of the actuating rod at the center of the drive piston, and comprising;
a shank portion extending rearward beyond the drive piston and centered on the axis of the drive piston.