GB2464112A

GB2464112A - Needle locking mechanism for a syringe

Info

Publication number: GB2464112A
Application number: GB0818059A
Authority: GB
Inventors: Abdul Khaliq Malik
Original assignee: Individual
Current assignee: Individual
Priority date: 2008-10-02
Filing date: 2008-10-02
Publication date: 2010-04-07
Anticipated expiration: 2028-10-02
Also published as: GB0818059D0; GB2464112B; WO2010038004A1; GB2464112A9

Abstract

The mechanism comprises a needle or cannula O having a ratchet collar R which in use engages a pawls PA1, PA2, PA3 located on an overhanging portion OH of a syringe body. In one embodiment the needle can be axially fitted onto the syringe with the pawls locking the needle and preventing rotational movement. In a further embodiment the ratchet R is arranged radially with pawls PR1, PR2, PR3 located around overhanging portion OH. A combination of these two embodiments is also disclosed. In use the mechanism prevents rotational movement and ejection of the needle from the syringe.

Description

I

Mechanism for the inhibition of the needle/cannula motion in disposable hypodermic syringes Disposable hypodermic syringes are used extensively in medical practice. An unassembled disposable syringe kit comprises two component parts: the needle/cannula and a piston-chamber (with piston already pre-assembled in it) (Fig.1). A syringe with a hypodermic needle is used in medical/surgical clinical applications, whereas a syringe with a cannula is used mainly in ophthalmology and other related clinical applications.

For the device to work as an integral syringe unit, first the needle/cannula must be interlocked into the piston-chamber. This is achieved in most cases, using a popular Luer-lock' type locking mechanism (Fig. 1). Here, a water-tight compressive seal between the plastic-cone C of the needle/cannula and the plastic exit nozzle N of the piston-chamber is formed, when the needle lug L' is screwed into the spiral groove G, cut into the overhung cylindrical section OH of the piston chamber.

The needle is secured in place, due to the combined frictional restraining forces setup at the compressive seal, and that between the needle lug L and the rib mn'of the spiral grooves (Fig.2).

However, an inadvertent failure of the Luer-lock has been reported [Refs. 1-7], where a sudden ejection of the needle/cannula as a projectile from a Luer-locked piston-chamber occurred under normal piston operational conditions. This raises serious safety doubts concerning the overall integrity of the Luer-lock arrangement, hitherto considered as safe' practice.

The accidental ejection of the needle/cannula from a syringe during any clinical procedure is froth with problems, and especially in clinical ophthalmology, it can lead to a catastrophic damage to the eye/tissue being treated.

It has been observed (Ref. 1) that during the needle fly-off in a Luer-lock syringe, the needle first rotates anticlockwise along the rib nm' (Fig.2), before acquiring an outward axial motion upon reaching the exit-end of the rib/groove. Also, that the ejection of the needle/cannula as a projectile during the normal pressurization phase of the piston occurs, mainly when the needle/cannula lug L during the initial coupling phase, is left short from its terminal lock-position (12O° ) and is retarded (Fig.3) within the position band (7O01O5o).

The use of the present invention prevents the axial fly-off of the needle/cannula as a projectile in a disposable syringe under normal piston operational conditions at all times, and overcomes the inherent deficiencies and safety-risks encountered in the Luer-lock mechanism.

The invention is a built-in mechanism within the syringe design, with inherent safety features. It provides a selective inhibition of the needle/cannula motion in any desired direction of the axial and/or rotational planes of the needle. These aspects of the invention may be realised as a separate individual operational feature or as a combined superimposed feature that restricts the needle motion in selected directions of both the axial and the rotational planes of the needle concurrently.

This invention also provides an easy push-fit' method of attaining a water-tight seal between the needle cone and the exit nozzle; once formed, the integrity of the seal is maintained by the ratchet-pawl arrangements that inherently inhibit any backward disruptive movement of the cone.

Besides attaining the above specific modes of operation, the invention may be adapted as a general controlling device either to permit or restrict the needle movement in any selected axial or radial direction.

The invention basically incorporates the ratchet-pawl principle within the design of the disposable syringe, where a single pawl or a number of pawis with multiple notches are made an integral part of the piston chamber and the needle incorporating an engaging collar with matching notches, acts as a dynamic ratchet. The profile-shape of the engaging and matching surface notches of the ratchet and the paw! is a simple saw-tooth (Fig.8). However the tips of the ratchet notches may be rounded (Fig.9), for an easy through-motion of the ratchet past the paw!s. The inhibition of the needle/cannula motion in any mutual plane and direction is dictated by the alignment and orientation of the ratchet-paw! arrangement i.e. the slope of the saw-tooth notches (Figs 7a & Th) within the selected plane.

Drawings: The following drawings relate to the description of the conventional Luer-lock arrangement used for the coupling of the needle and the piston-chamber in disposable syringes: Figs. 1 illustrates the cross-sectional view of the needle and the piston chamber of a typical conventional disposable hypodermic syringe with a Luer-lock coupling arrangement.

[Needle/cannula comprises: 0 -small bore metallic needle/cannula, C -plastic needle cone & L -needle lug. Piston chamber comprises: N-exit nozzle, OH-overhung cylindrical portion of the piston chamber, G-spiral grooves & T-pistonj Fig.2 illustrates the details of the Luer type lock arrangement.

[For coupling: the needle-cone lug L is screwed clockwise along the rib mn' within the spiral grooves GJ.

Fig.3 illustrates the cone-lug position, for a perfect' and imperfect' coupling' between the needle/cannula and the piston exit-nozzle.

[Perfect-coupling: needle lug at end-terminal position i.e. at 120° position within the groove; needle is securely locked at this position and does not fly-off as a projectile under norma/piston operational conditions. imperfect-coupling: needle lug within 700l 050 zone and the needle flies off as a projectile under norma/piston operational conditionsj The following drawings describe the working principle of the ratchet-pawl arrangement of this invention, as incorporated in the design of disposable hypodermic svrnges. to exert control on the motion of the needle/cannula: Fig.4 depicts the piston-chamber Q with an extended cylindrical overhung portion OH of the piston-chamber for the accommodation of the integrated pawis.

Fig. 5 illustrates an axial ratchet-pawl arrangement.

[A & S two components of the paw!, R: engaging ratchet arranged as a collar around needle barrel B, C-needle cone, N -piston exit-nozzle, 0-metallic needk/cannulaJ Fig.6 illustrates the details of an axial Paw! (PA).

[One end of the cantilever' type paw! arm A', stationary and imbedded in the body of the syringe OH, S: the flexible end of the arm provided with engaging saw-tooth like notches.

The direction of motion of the dynamic ratchet R determined by the alignment and orientation of the saw-tooth notches].

Fig 7(a) Illustrates the engaging and matching saw-tooth like notches of the ratchet-paw! arrangement aligned L' to R' [The slope ab' of the saw-tooth determines the orientation and alignment of the ratchet-paw! arrangement] Fig. 7(b) Illustrates the engaging and matching saw-tooth like notches of the ratchet-paw! arrangement aligned R' to L' Fig. 8 illustrates the mechanical equivalent representation of an axial ratchet-pawl arrangement.

[Arm 4 represents a mechanical spring] Fig.9 illustrates the rounded saw-tooth notches.

Fig. 10 illustrates the mechanical equivalent representation of a radial ratchet-pawl arrangement.

Fig. 11 shows the relative radii and radius of curvatures for the various components of an axial ratchet-pawl arrangement.

The following drawings relate to the description of the axial pawls and their role in inhibiting axial motion of the needle: Fig. 12 illustrates an isometric view of a disposable syringe that restricts outward axial motion of the needle.

[The saw-tooth notches run circumferentially along the curved surface of the ratchet].

Fig.13 is a cross-sectional view AA' on Fig.12.

[Illustrates an arrangement of three pawis (PA1, PA2, and PA3 equally spaced 120 degrees apart as an integral part of the overhung portion of the piston chamber OH. R: common ratchet an integral part of the needle].

Fig. 14 is a cross-sectional view BB' on Fig 13.

[Ratchet section R of the needle engaging with the paw/s. shown as an isometric presentation, and the cone section C as a cross-sectional view. N -piston chamber exit-nozzle, T -piston].

Fig.15 illustrates the piston-chamber with three axial pawls (PAl, PA2 & PM) and the positional radius of the pawis.

Fig. 16 illustrates the design of an axial ratchet.

[C: needle cone, R: Ratchet, as a collar around the needle barrel B] Fig.17 illustrates the 3-D view of a typical axial ratchet.

The following drawings relate to the description of the radial pawls and their role in inhibiting the rotational motion of the needle: Fig. 18 illustrates an isometric view of a disposable syringe that inhibits anti-clockwise rotation of the needle.

[Ratchet notches run axial along the surface of the collar].

Fig. 19 is a cross-sectional view AA on Fig. 18.

[illustrates an arrangement of three radial paw/s PR1, PR2 & PR3 equally spaced 1200 degrees apart, and as an integral part of the body of the piston chamber OH. R: a common ratchet also an integral part of the needle/ccmnula].

Fig.20 is a cross-sectional view BB on Fig 19. It illustrates, radially aligned pawis (PR1, PR2, PR3), the water-tight compression-seal between the needle-cone C and the piston-chamber exit nozzle N, and the needle lug L screwed within the spiral groove G. [Ratchet R, engaging with the pawis illustrated as an isometric presentation, and the cone C shown in a cross-sectional view. N: piston-chamber exit-nozzle, G: spiral groove, L: needle lug, T: -piston].

Fig.21 shows the piston-chamber with three radial pawis (PR1, PR2 & PR3) positioned 120 degrees apart along the inner circumference of the overhang cylinder.

Fig.22 illustrates the details of a radial ratchet collar positioned between the cone C and the metallic needle/cannula. 0.

IL: needle lug].

Fig.23 illustrates the 3-D view of a radial ratchet.

Fig.24 shows the details of a lug and spiral-groove' mechanism, an additional requirement to radially aligned ratchet-pawl arrangement for the formation of water-tight seal between the cone and the piston nozzle The following drawings relate to the description of the combined radial and axial pawis. and their role in simultaneously inhibiting the rotational and the axial motion of the needle: Fig.25 illustrates a composite ratchet-pawl arrangement for simultaneous inhibition of outward axial and the anticlockwise rotational motion of the needle/cannula.

[PRI, PR2 & PR3: radial pawis. PA], PA2 & PA3: axial paw/s. Common engaging ratchet R is shown as an isometric presentation, and the cone C as a cross-sectional view.

N: piston exit-nozzle, T: piston].

Fig.26 illustrates the relative location of the three axial and three radial pawis within the overhung cylindrical piston-chamber.

Fig.27. illustrate a composite axial and radial ratchet.

Fig. 28 illustrates the 3-D view of a composite ratchet.

The following drawings describe the rig for the fabrication of a single axial pawl: Fig.29 illustrates an outline of a rig for the fabrication of the piston-chamber with a single axial pawl (PA) as an integral component.

[3, 4, & 5 are the three main component parts] Fig.30 illustrates the cross-sectional view AA in Fig 29 [Leg 3L and side-wing 5F tight-fit' inserts within the window xx' cut in 4] Fig.3 1 illustrates the structural details of the three main components 3, 4 and 5 of the rig.

Fig.32 illustrates the details of an assembled rig for the fabrication of a single axial pawl (PA).

Fig.33 illustrates the design of the side-wing 5F appropriate for the fabrication of a single axial pawl PA.

[PA engraved hollow' replica of the desired axial paw! cut in the Side-wing 5F, solidly coupled to the central shafts. x the endface of shaped cylinder 4].

The following drawings describe the rg for the fabrication of multiple (three) axial pawis: Fig.34 illustrates the cross-sectional view of the rig for the fabrication of multiple axial pawls.

[A cross-sectional view along AA' in Fig 32, taking into account the additional requirements for the fabrication of three paw/s PA1, PA2 and PA3]..

Fig.35 illustrates the cross-sectional view BB in Fig.34.

Fig.36 illustrates the shape of a specific window cut in cylinder 4, necessary for the fabrication of multiple axial pawls.

[Three identical windows xx' are cut 120 degrees apart within the cylinder 4].

The following drawings describe the rig for the fabrication of radial pawls: Fig.37 illustrates a rig for the fabrication of a single radial pawl (PR), and the spiral grooves G..

The lower end G of central shaft 10, facilitates the formation of the water-tight seal between the needle cone and the exit-nozzle in conjunction with needle lug G, when a water-tight seal between the cone and the nozzle is a requirement] Fig.38 illustrates in detail the description of an assembled rig for the fabrication of a single radial paw! PR, spiral groove G and needle cone N. Fig.39 illustrates the cross-sectional view EE in Fig.38.

[Side-wing 5F is coupled to the hollow shaft 5. Leg 3L and the side-wing 5F perfect-fit' within the window space xx 7.

The following drawings describe the rig for the fabrication of combined axial and radial paw!s: Fig. 40 illustrates a rig for the fabrication of both axial PA and radial PR pawls as integral parts of the overhung cylindrical portion of the piston chamber.

The following drawings describe the rig for the fabrication of an axially aligned ratchet: Fig.41 illustrates one-half of the rig for the fabrication of an axial ratchet R. Fig.42 illustrates the cross-sectional view AA on Fig.4 1.

Detailed description of the invention:

i) The principle of operation of the ratchet-pawl mechanism of the invention, as incorporated within the design of disposable syringe assembly, for the control of the needle/cannula motion.

The invention invokes the concept of mechanical ratchet and paw! mechanism, and incorporates its underlying principles within the design of the needle/cannula and the piston-chamber of the conventional disposable hypodermic syringe. Specifically, the ratchet and the paw! flinctions are assimilated within the design of the needle/cannula and the piston chamber respectively as illustrated in Fig.5. Here, OH is the overhung cylindrical portion of the piston chamber (Fig.4). The ratchet R is a collar, arranged over the barrel B of the needle/cannula, and provided with saw-tooth like surface engaging notches. C is the needle cone, N the piston exit-nozzle and 0 is the small bore metallic needle/cannula.

The paw! (illustrated as aligned in the axial plane of the needle/cannula in Fig.5 and identified as PA' in Fig.6) is arranged as a cantilever, comprising a short arm A and an engaging (grabbing) end S. The fixed end of the cantilever/arm A (Figs 5 & 6) is embedded within the body of the over-hung cylindrical portion OH, and is therefore stationary with respect to the mutual (axial and rotational) planes of motion of the needle/cannula. The flexible' end S of the pawl engages with the ratchet R, and flexes through a small outward amplitude for any applied force such as that arising from the inward axial motion of the ratchet. 5' is also provided with a set of engaging saw-tooth like notches, pointing down towards the central axis. Multiple notches ensure enhanced contact with the ratchet, but a single notch would also be sufficient.

A similar argument applies for a pawl aligned in the rotational plane of the needle/cannula (Fig. 10).

Fig 8 depicts the mechanical equivalent representation of a typical axial ratchet-paw! arrangement.

Here the arm A of the paw! represents a mechanical spring, and depending on the nature of the applied force it either acts as a simple cantilever or a stiff spring in compression. For an axial motion of the ratchet along the direction of the alignment of the arrangement (i.e. in the direction of the arrow as indicated), the arm A behaves as a cantilever. Its flexible end is displaced upwards, and the ratchet moves past the pawl-notches unimpeded.

For force acting against the alignment of the arrangement, the vertical edge of the saw-tooth of the ratchet notch engages against the vertical face of the pawl-notch, and the arm A is driven in compression, and the ratchet (i.e. the needle) motion is impeded.

The width w' of the saw-tooth notches S of the axial paw! PA (and also that of the radial pawl) is fmite (Figs.6 & 11), in order to ensure a reasonable contact area between the engaging ratchet and the pawl components.

However, adjustment of the various dimensions of the ratchet and the pawl as indicated in Fig. 11, determine the overall resistance of the ratchet (or the syringe needle) past the pawl. Here, r and r2 represent the lower and the upper radii of the ratchet saw-tooth notches, and R and R represents the curvature of the engaging paw! notches.

Reduced curvatures R and R1, of the paw! notches stiffen the through-put motion of the needle, whereas enlarged curvatures lead to an easy motion. Thus curvatures R and R may be altered to achieve a desired degree of friction between the ratchet and the pawis.

A set of three pawls distributed 120 degrees apart around the circumference of OH provide stability and symmetry to the ratchet (needle). Also, any backlash and play' between the engaging notches may be overcome by staggering the three pawls axially in a vernier fashion.

The profile of the engaging and matching notches for both the pawl S and the ratchet R are saw-tooth-like as illustrated in Figs 5, 6, 7, and 10).

The saw-tooth-like notches on the surface of an axial-ratchet that engage with their counterparts in the axial-pawls, run circumferentially (Figs.5) and extend over the entire curved surface of the collar. Similarly, the notches for a radial-ratchet are cut and run axially (Figs 22 & 23) over the entire curved surface of the needle collar.

In a ratchet-pawl arrangement with a cantilever type pawl (with one end fixed), and where the saw-tooth like notches of the pawl engage and match that of the ratchet, the slope' of the notches determine the permissible direction of motion of the ratchet. In Fig.7a, the slope of the saw-tooth notches is from L' to R', thus under appropriately directed applied force, the ratchet can only move from L' to R' direction, and its motion R' to L' is always inhibited. Similarly in Fig.7b, the slope of the saw-tooth notches is from R' to L, thus the permissible direction of motion of the ratchet is from R' to L' and its motion from L' to R' in this particular case is inhibited.

In the present context, an axial-pawl' or axially aligned pawl' (Figs.5 & 6), implies that the length of the pawl arm A is in the axial plane and the slope' of the saw-tooth notches point inwards, towards the exit nozzle of the piston-chamber. Similarly for a radial-pawl' or radially aligned pawl', the arm A is in the radial plane of the needle/cannula with the slope' of the saw-tooth notches pointing in clockwise radial direction (Fig.10). The permissible rotational motion of the ratchet (i.e. the needle/cannula) in this configuration is in the clockwise direction. The ratchet rotation in the anticlockwise direction in this particular case is inhibited.

Also in the present context, axial' ratchet-paw! arrangement implies that the slope' of the saw- teeth of both the pawl and the ratchet point axially inwards i.e. toward the exit nozzle of the piston -chamber. Thus the permissible motion of the ratchet is axially inwards i.e. towards the exit nozzle of the piston-chamber, and an outward axial motion of the ratchet is inhibited.

Similarly, a radial' ratchet-paw! arrangement implies that the slope of the saw-teeth of the pawl and the ratchet both point in the clockwise radial direction and the permissible ratchet motion is also in the clockwise radial direction; and the rotation of the ratchet/needle in the anticlockwise direction is inhibited.

ii) Inhibition of outward axial motion of the needle For this function, three axially aligned pawis PA1, PA2 and PA3 (Figs.13&14) spaced circufrentially 120 degrees apart along the inner surface of the cylindrical overhung OH section of the piston chamber, are used. The three pawis engage with a common ratchet R arranged as a collar on the needle-barrel B and located between the cone C and the narrow-bore discharge metallic capillary tube 0 (Fig. 16). The engaging surface notches of both the ratchet and the pawis are saw-tooth like with the sloping-edge of the saw tooth notches pointing axially inwards i.e. towards the exit-nozzle of the piston-chamber (Figs 14,16 &17). The surface profile of the engaging notches of both the ratchet and the pawls can be a simple saw-tooth (Fig.8) or for an easy manoeuvrability, the sloping section of the ratchet surface alone is curved as shown in Fig.9.

The position radius of the pawls Rp (fig. 15) exceeds the inner radius RD of the piston-chamber containing the needle-cone, simply to facilitate the fabrication of the various pawis and other components within the piston-chamber. The axially aligned pawls PA1, PA2 and PA3 are an integral part of the cylindrical over-hung portion OH of the piston-chamber (Fig. 15). As already discussed in sect. ii), a ratchet-pawl arrangement aligned inwards in the direction of the exit-nozzle of the piston, inhibits any outward axial motion of the needle (ratchet) at all times.

Also in this configuration, pushing the needle-cone against the exit nozzle in conjunction with axial ratchet-paw! arrangement attains a water-tight compressive seal between the needle-cone and the exit nozzle of the piston-chamber. (The system permits an application of both axial force and clockwise twist on the cone, and both manoeuvres are useful in attaining a water-tight seal between the cone and the nozzle).

The integrity of this seal is maintained by the ratchet-paw! arrangement that inherent!y inhibits any backward movement of the needle at all times.

iii) Inhibition of anticlockwise rotational motion of the needle.

For this configuration, three radially aligned pawls PR1, PR2 and PR3 (Figs. 19 & 20) spaced circumfrentially 120 degrees apart at the outer edge and along the inner surface of the cylindrical overhung section OH of the piston chamber are used. The pawls engage with a common ratchet R arranged as a collar on the needle-barrel B, and located between the cone C and the narrow-bore discharge metallic tube 0 (Figs.22 & 23). The engaging surface notches of both the ratchet and the pawls are saw-tooth like, with the sloping' edge of the saw tooth notch of the pawls aligned along the clockwise rotational direction of the needle (Fig. 19). The surface profile of the engaging notches of both the ratchet R and the pawls (PR1, PR2 and PR3) can be a simple saw-tooth (Fig.8) or for an easy manoeuvrability, the sloping section of the saw-tooth part of the ratchet surface alone, is curved as shown in Fig.9.

The radially aligned pawls PR1, PR2 and PR3 form an integral part of the cylindrical over-hung portion OH of the piston-chamber (Figs.19 & 21).

During forced clockwise rotational motion of the needle (or ratchet R), the pawls are displaced radially outwards and the clockwise rotation of the needle is unhindered. However, during anti-clockwise rotation of the needle, the vertical face of the notch of the ratchet, locks against the vertical face of the paw! notch, and the arm A (Fig. 10) is driven in compression and the anticlockwise rotation of the needle is inhibited.

Thus this arrangement prevents any anticlockwise rotation of the needle within the syringe and is particularly useful in preventing needle fly-off as a projectile in Luer-lock-type disposable syringes, where an anticlockwise rotation of the needle is known [ref 1] to act as a precursor to the subsequent fly-off' of the needle as a projectile in the axial direction.

The radial ratchet-pawl arrangement, however on its own does not facilitate the formation of a water-tight seal between the needle-cone and the exit-nozzle of the piston chamber. To achieve this, the needle cone must be forced onto the nozzle, by screwing (clockwise) cone tugs L, into the spiral grooves G cut into the body of the piston-chamber (Fig.20). For this purpose, an improved design of lugs as illustrated in Fig.24 is suggested. Here a substantial surface area of the lug L makes contact with the lower rib mn' of the groove G, resulting in increased contact frictional resistance, thus reducing the chances of anticlockwise rotation of the needle/cannula. This design is totally different from the conventional Luer-lock type arrangement, where only the edge of the lug L makes a point contact with the rib mn' or qq' and the frictional resistance to needle rotational motion is minimal (Fig 2).

iv) Simultaneous inhibition of both anti-clockwise rotation and outward axial motion of the needle/cannula.

For this configuration, both the radial pawls (PR1, PR2 and PR3) and the axial pawis (PAl, PA2 and PM) are made an integral part of the cylindrical overhung portion of the piston chamber OH as shown in Figs 25 and 26. R' acts as a common ratchet. The ratchet surface is provided with a saw-tooth like surface notches cut and aligned axially inwards (i.e. towards the piston exit nozzle), superimposed with another set of saw-tooth notches arranged and aligned radially clockwise as indicated in Figs. 27 and 28.

To inhibit the needle-motion in both outward axial and anticlockwise rotational directions concurrently the axial pawis are aligned inwards (i.e. towards the piston exit-nozzle), and the radial pawis are aligned along the clockwise rotational direction of the needle.

In the present configuration, a water-tight seal between the needle cone and the exit nozzle is formed when the needle is pushed through the axial pawis and is forced onto the exit-nozzle. The system permits both axial inward and clockwise rotation of the needle, and these are useful in attaining a water-tight seal. The combined axial and radial ratchet-pawl arrangement, prevent any outward axial and anticlockwise rotational movement of the needle/cannula, and thus the integrity of the seal, once formed, is maintained.

Fabrication techniques for the various components appropriate to the invention: a) Fabrication of a single axial pawl The fabrication of the plastic piston chamber Q and its cylindrical overhung portion OH (Fig. 1) without the pawls, is a well established industrial procedure. However, the moulding of OH (Fig.4) with an axial pawl PA as an integral part is novel and may be achieved using a special rig as described in figs 29-35 inclusive. However, the main difficulty in this procedure is the extraction of the pawl forming metallic bits and pieces from within the piston chamber after the completion of the plastic injection/moulding procedure.

Figs 29 & 30) depict a concentric arrangement of a central shaft 5 arranged within shaped and sliding cylinders 3 & 4. Fig 30 is a cross-sectional view of the arrangement on Fig. 29.

Fig.3 1 illustrates the shape of the various individual components 3, 4 and 5.

A solid cylinder 3 with a central bore is shaped as shown in Fig.31, where 3L is an integral but protruding leg in the shape of a cylindrical segment. The cylinder also carries a short upper cylindrical neck 3T.

The central shaft 5 (Fig.3 1) carries a side-wing SF in the shape of a cylindrical segment, located approximately halfway along the length of 5. The side-wing 5F is slotted-in and fixed to the shaft 5.

16 is a base collar on shaft 5 and provide support for the arrangement of cylinders 3 and 4. The lower end N of shaft 5 conforms to the desired shape of the needle cone, and a subsidiary cone-forming shaft 7 (Fig.32) screws into it.

The cylinder 4 is C' shaped as shown in Figs 30 and 31. The leg 3L and the side-wing SF are a perfect fit' within the window space xx' in the cylinder 4 (Fig.30).

In a frilly assembled state, the various individual components 3, 4 and 5 assume the shape of concentric cylinders (Figs.29 & 32). Here 13 is the outer casing/wall of the rig. 7, a subsidiary shaped cylinder, aid the formation of the needle/cannula cone.

Fig.33 illustrates the interface between the side-wing 5F of the central shaft S and the end face of the cylinder 4. The shape and size of the desired axial pawl PA' is engraved as a hollow' cut within the face abbd' of the side-wing SF. The hollow' cut is located at the outer edge bb' of 5F.

During the plastic moulding, this forms the fixed end of the pawl arm A connected to the body of the overhung portion OH of the piston chamber (Fig.6). The face abbd' of the side-wing segment 5F mates against the smooth and flat surface x' of the cylinder 4 (Fig.33).

After the completion of the plastic injection/moulding procedure, the cylinder 3 is first lifted upwards through Ax (Fig.32) to lock into shaft 5 via 8 and 9. The lifting of 3, lifts the leg 3L, from the space cc' in cylinder 4, creating an empty space adjacent to the side-wing SF (Fig.30). Shaft 5 is then rotated clockwise, and this in turn rotates the side-wing 5F into the empty space previously occupied by leg 3L, and clear from the formed PA. The moulded pawl PA is now clear from any obstructions and all the metallic bits and pieces can be lifted clear out of the chamber with pawl intact as an integral part of the piston-chamber OH, by further pulling out the coupled shat 5 and 3T arrangement.

2' and 12' in Fig. 12 are guide rods and slots for the arrangement.

The whole procedure for the extraction of the pawl-forming bits and pieces from within the fabricated piston chamber, may be automated as a sequence (with reference to Fig.32): First, i) Unscrew the subsidiary shaft 7 from N ii) Lift 3 upwards through Ax [this locks 3 (or its integral portion 31) into 5, via interlocking system 8 and 9, and also creates an empty space adjacent to SF] iii) Turn 5/3T clockwise. [This rotates the segment SF clear from the formed pawl PA].

iv) Pull 5/3T upwards [This retracts all the pawl-forming bits and pieces from the chamber].

b) Fabrication of multiple (three) axial pawis The foregoing system (sect. a) is used for the fabrication of a single axial pawl PA.

The rig described in Figs 34 and 35, is used for the fabrication of three axial pawls PA1, PA2 and PA3 spaced 120 degrees apart. Fig 34 is a cross-sectional view AA on Fig.32, making provisions for three pawls. The cylinder 3 (Fig.3 1) is now provided with three legs 3L1, 3L2 and 3L3 spaced degrees apart. The central shaft S (Fig.3 1) is also provided with three side-wings SF1, SF2 and SF3, 120 degrees apart. The hollow cylinder 4 now has three cut-out windows xx', spaced 120 degrees apart, instead of just an open slot xx' sufficient for the fabrication of a single axial pawl PA (Fig.31).

Fig. 36 illustrates the design of the window xx' cut within the curved surface of the hollow cylinder 4 for the fabrication of multiple axial pawls. For the fabrication of three windows, the process is simply repeated at 120 degree interval. Each window is dimensioned such as to accommodate respective combination of leg plus side-wing component parts i.e. (3L1+SF1), (3L2+5F2) and (3L3+5F3) within the window spacing xx', and the component inserts are a perfect fit' within the windows. During assembly, the side-wings 5F1, 5F2, 5F3 are fixed to the shaft 5 last, gaining access to the slot in shaft S via the cutaway window spaces in cylinder 4.

Fig.35 is a cross-sectional view BB' on Fig 34. It illustrates the interconnection of the central shaft with the side-wing 5F1, the relative position of the leg 3L2, and the position of the cylinder 4, the supporting collar 6, and the preferred location of the hollow' cut PA1 cut within SF1 for the fabrication of the axial pawl PA1. Fig.34 illustrates an assembled rig arrangement.

The procedure for the removal of metallic pawl forming bits and pieces after the completion of the fabrication procedure remains the same as already described in (sect. a, Fig.32) for the fabrication of a single axial paw!. It is noteworthy that in this particular configuration, the spiral grooves G and the associated needle lug arrangement is not needed for the formation of the water-tight seal between the needle-cone and the exit-nozzle of the piston chamber. The water-tight seal is formed, by just forcing the needle axially inwards, through the engaging ratchet-paw! arrangement, onto the piston exit-nozzle and twisting it clockwise. Once formed, the integrity of the seal is maintained, as the axial ratchet-pawl arrangement inherently restricts any outward axial motion of the needle.

To overcome any backlash or play that may exist between the engaging saw-tooth notches (that may affect the water-tight seal adversely), the relative axial position of the three pawis PA1, PA2 and PA3 may be finely staggered as a vernier arrangement to overcome the problem.

c) Fabrication of Radial Pawis The rig for the fabrication of a radial pawl is similar to that already described for the fabrication of the axial pawis (Figs.29-35), except that in the present case the hollow' cut (to facilitate the formation of the desired radial pawl PR), is cut in the underside of disc 3, at a location that also embraces the top surface of the side-wing 5F (Fig.37). This permits PR to sit just above the flat and smooth upper solid surface of the side-wing segment 5F.

Fabrication of a radial pawl however, does not facilitate the formation of the water-tight seal between the needle-cone and the exit-nozzle of the piston chamber. When this is a requirement, then the arrangement of four concentric components as shown in (Figs.37&38) are used, instead of the three component configuration appropriate for the formation of an axial pawl (Fig.29).

Here, the central shaft 10 (Fig 37) is used as an independent item (arranged as an inner most item within the rest of the outer rig) for the fabrication of the necessary spiral grooves G and the needle cone N. The shaft 5 is now hollow and connects to the side-wing segment 5F as shown in Figs 38 &39.

After the completion of the plastic injection/moulding procedure, the disc 3 is lifted upwards through a distance Ax, in order to create an empty space adjacent to the side-wing (5F) and also to clear 3' away from the formed pawl PR (Fig.38). In the process, 3 locks into 5 via the interlocking system 8 and 9. Next, the tube 5 is rotated clockwise, and in the process the interconnected segment 5F is pushed into the vacant space created by the previous removal of 3L. This also clears SF away from the underside of the formed PR. Finally, the whole forming-Contraption is pulled out of the mouldings to yield OH with a radial pawl as an integral component of the piston-chamber. In Fig.38, the outer casing (such as that indicated in Fig.32) is necessary for the fabrication purposes, but here it has been omitted to avoid cluttering of the drawing.

The system is easily adaptable for the fabrication of multi (three) radial pawis, using the concepts of the rig described in Figs 34, 35 and 36 for the fabrication of three axial paw!s.

d) Fabrication of combined radial and axial pawis The rig described in Fig.40 may be used for the combined fabrication of a single axial (PA) and a single radial (PR) pawl. The hollow' for the formation of the radial paw!, is cut within the underside of the disc 3 at a location that also embraces the upper face of the side-wing segment 5F.

The hollow' for the formation of an axial paw! is cut within the vertical face of 5F interfacing against the end face of 4 as illustrated in fig 40.

The saw-tooth notches of both the axial and the radial pawis are located at a common positional radius. The fabrication-procedure otherwise is the same as that described for the fabrication of the axial pawis (Fig.32).

A set of three axial and three radial pawis may also be fabricated; combining the fabrication techniques already described (Fig.34) for three axial pawls separated 120 degrees apart, taking into consideration the above requirements.

An arrangement of combined multiple axial and radial pawls, because of the inclusion of the axial arrangement, facilitate the formation of the water-tight seal between the needle-cone and the piston chamber exit-nozzle. Thus in this particular configuration, there is no need for the spiral grooves G' and the needle/cannula lug L (Fig 24), specifically intended for attaining the seal e) Fabrication of the ratchet Figs 41 and 42 illustrate a rig for the fabrication of an axial ratchet. Here the die-cuttings for the formation of the saw-tooth notches for the ratchet R, are radial; and C represents the cone section of the needle.

A similar rig may be used for the fabrication of a radial ratchet, where the cuttings in the die for the fabrication of the saw-tooth notches would run in an axial direction.

For the formation of a common ratchet to interface with a combination of both axial and radial pawis, the radial cuttings within the appropriate portion of the Die' are superimposed onto the radial cuttings.

References 1. Malik A, Zia R, Patel K. Accidental Ejection of a cannula from Luer-locked syringe during wound hydradation process, causing IOL drop, Vitreous Loss and Haemorrhage. XXVI Congress of the European Society Cataract and Refractive Surgeons, Berlin Sept, 2008; Complex Cataract, Paper: 410.00 2. Fletcher S J. Failure of a Luer-lock. Anaesthesia 2005; 60(2): 206.

3. Holmes K., Snow D., et at. More problems with Luer-lock connections. Anaesthesia 2006: 61(1): 72-73.

4. Osher R. Iris damage by inadvertent cannula injection. J. Cataract Refract. Surg. 2006; 33(2):339-341.

5. Gupta D, Burton B et at. latrogenic retinal detachment due to cannula slippage despite use of Luer-lock syringe system. J Cataract Refract. Surg. 2008:34(9): 1612.

6. Two-piece Luer-lock may not be locked'. Health Devices 2000; 29(5):190-1.

7. Equipment failure: Luer-lock'. Anaesthesia Intensive Care 1987;15(2):249.

Claims

Claims 1. A mechanism for the coupling of the needle/cannula to the piston-chamber in a disposable hypodermic syringe, incorporating the ratchet-pawl principles in the design of the needle/cannula and the piston chamber, in order to selectively, either inhibit or permit the needle/cannula motion in any desired mutual plane and direction, and also to facilitate the formation of the water-tight seal between the needle/cannula cone and the exit-nozzle of the piston-chamber..
2. A coupling mechanism for the needle/cannula and the piston chamber in a disposable hypodermic syringe according to 1, where a cantilever type pawl (or pawls) aligned in the axial plane with its fixed end imbedded within the body of the piston-chamber, and the saw-tooth like engaging (grabbing) notches at the flexible end pointing inwards i.e. towards the piston exit-nozzle, in conjunction with an engaging ratchet arranged as a collar around the needle/cannula barrel and also provided with matching surface saw-tooth notches, inhibit any outward axial motion of the needle/cannula.
3. A coupling mechanism between the needle/cannula and the piston chamber in a disposable hypodermic syringe according to 1, where the desired direction of the needle/cannula motion or its inhibition in the axial plane is determined by an appropriate alignment and orientation of the saw-tooth engaging notches of the ratchet-pawl arrangement in this plane.
4. A coupling mechanism for the needle/cannula and the piston chamber in a disposable hypodermic syringe according to 1, where a cantilever type pawl (or pawls) aligned in the radial plane with its fixed end imbedded within the body of the piston-chamber, and the saw-tooth like engaging (grabbing) notches at the flexible end aligned in clockwise direction, in conjunction with an engaging ratchet arranged as a collar around the needle/cannula barrel provided with matching surface saw-tooth notches, inhibit any anticlockwise rotation of the needle/cannula.
5. A coupling mechanism between the needle/cannula and the piston chamber in a disposable hypodermic syringe according to 1, where the desired direction of the needle/cannula motion or its inhibition in the radial plane is determined by an appropriate alignment and orientation of the saw-tooth engaging notches of the ratchet-pawl arrangement in this plane.
6. A coupling mechanism between the needle/cannula and the piston chamber in a disposable hypodermic syringe according to 1, where the ratchet-pawl arrangement(s) of claims 2 and 4 either individually or collectively, prevent the risk of needle/cannula fly-off as a projectile in disposable hypodermic syringes under normal piston operational conditions.
7. A coupling mechanism between the needle/cannula and the piston chamber in a disposable hypodermic syringe according to 1, where the ratchet-pawl arrangement(s) of claims 2 and 4 either individually or collectively, prevent the risk of inadvertent needle/cannula fly-off as a projectile in Luer-lock type disposable hypodermic syringes.
8. A coupling mechanism between the needle/cannula and the piston chamber in a disposable hypodermic syringe according to 1, where the ratchet-pawl arrangement(s) of claim 2 facilitate the formation of the water-tight compression seal between the needle/cannula cone and the exit-nozzle of the piston chamber, using simple needle axial push and to-and-fro twist manoeuvres.
9. A coupling mechanism between the needle/cannula and the piston chamber in a disposable hypodermic syringe according to 1, where the ratchet-pawl arrangement(s) of claims 2 and 4 collectively facilitate the formation of the water-tight compression seal between the needle/cannula and the exit-nozzle of the piston chamber, using simple needle axial push and clockwise twist manoeuvres.Amended claims have been filed as follows:-What is claimed: 1. A syringe with an integral ratchet-pawl mechanism comprising: i) a barrel having a fluid chamber, a proximal end, a distal end and a frusto-conical tip extending outwards from the said distal end having a passageway there through in fluid communication with said chamber, a collar at the distal end of the barrel surrounding said conical tip and incorporating: (a) at the distal end at least one flexible cantilevered paw! with its proximal end buried within the body of the syringe collar and the cantilevered arm extending axially inwards towards the said syringe barrel at an oblique angle to the collar and with a shoe at its distal end incorporating several saw-tooth like teeth at its underside cut as circumferential arcs aziniuthaily and with the saw-teeth slopping' pointing inwards towards the said syringe barrel, to engage with a mating ratchet wheel surface incorporated within the needle/cannula assembly as described here under, and (b) a pair of smooth pegs or a short curved surface incorporated within the syringe collar and in line with the said shoe to stabilise/centralise the needle/cannula assembly; and ii) a needle/cannula assembly comprising: a) a metallic needle/cannula capillary having a proximal end, a distal end and a lumen there through, a hub having an open proximal end with a cavity therein, and a distal end joined to said proximal end of said metallic capillary so that said lumen is in fluid communication with said cavity, and : * b) a hub comprising a cylindrical section terminating into a conical section at the proximal end, and . : c) a ratchet wheel at the distal end of the cylindrical section of the said * *. hub and arranged orthogonal to the axis with the engaging surface teeth cut circumferentially and the sloping' section' of the teeth pointing axially inwards towards the said barrel, to engage with its said **** pawl shoe counterpart incorporated within the said syringe collar, p.. S * . the said needle/cannula assembly being connected to the said barrel whereby: a) as the said ratchet wheel at the said hub of the said needle/cannula is treaded through to engaged with its counterpart shoe of the said cantilever paw! of the said syringe collar of the said barrel thereby permits an inward axial and free rotational motions of the needle/cannula, and thereby prevents any subsequent outward axial motion of the need le/cannula, and b) as the said conical hub of the needle/cannula assembly is pressed against the said conical tip of the barrel, a fluid-tight compressive seal is forms consequent to applied inward axial force and to and fro rotational twists to the said needleicannula, thereby providing a passageway there through in fluid communication from the barrel chamber to the needl&cannula tip; and iii) a plunger including an elongated plunger rod having a longitudinal axis for drawing fluid into and out of said chamber by movement of said plunger relative to said barrel.2. The syringe of claim 1 4iereby the means of providing a built-in mechanical safety against an accidental outward axial fly-off of the needle/cannula as a projectile under normal piston operation in disposable syringes includes the said integral ratchet-pawl mechanism operating in an axial plane/mode.3. The syringe of claim 1 wherein a plurality of pawls comprises at least three pawls distributed equally circumferentially along the internal surface of the said collar of the barrel and all pawl shoes engage with a common ratchet of the said hub of the needle assembly and thereby eliminate the need for the said stabilising/centralising pegs or curved surface segment for the said needle/ cannula assembly.4. The syringe of claim 3 whereby the means of providing a built-in mechanical safety against an accidental outward fly-off of the needle/cannula as a projectile under normal piston operation in disposable syringes includes the said integral ratchet-pawl mechanism with plurality of said cantilevered pawls operating in an axial plane/mode.5. The syringe of claim 3 whereby the means of providing both a mechanical means of attaining a compressive fluid-tight seal between the needle/cannula and the syringe barrel and also a built-in mechanical safety against an accidental outward fly-off of the needle/cannula as a projectile under normal piston operation in disposable * syringes includes the said integral ratchet-paw! mechanism with plurality of said cantilevered pawls operating in an axial plane/mode.6. The syringe of claim 3 wherein the requisite mechanical coupling between the * needle/cannuJa and the syringe barrel is attained through the said ratchet-p awl mechanism operating in an axial plane/mode and thereby eliminate the need for the conventional Luer-lock type locking tabs within the needle/cannula and the spiral grooves within the underside of the said syringe collar in disposable syringes. ***7. The syringe of claim 6 wherein the plurality of axially aligned-pawl-ratchet arrangement leading to a fluid-tight seal between the conical tip of the barrel and the hub of the needle thereby eliminates the need for any additional or subsidiary mechanism for such purposes in disposable syringes.8. The syringe of claim 3 wherein at least one cantilever pawl comprises a plurality of pawls dispersed circumferentially and the pawl shoes displaced relative to each other axially provides a vernier mode of operation, useful to accommodate the variability in component manufacturing dimensional tolerances.9. The syringe of claim 1 wherein at least one ratchet-paw! in an axial mode prevents uncoupling of the needl&cannula from the syringe barrel after initial use and thereby satisfS' the healthcare directives for disposal of syringes under such conditions.
10. A syringe whereby an axial and azimuthal modes of operation of the ratchet-paw! of claim 3 and claim 4 (of the ratchet-paw! arrangement in azimuthal mode: GB 0818059.8) respectively are combined to provide an enhanced inhibition of outward axial motion of the need!e/cannula in disposable syringes.
11. The syringe of claim 1, whereby the means of providing a fluid-tight seal between the conical hub of the needle/cannu!a and the conical tip of the syringe for the transfer of fluid, and also a built-in mechanical safety against any accidental outward fly-off of the needle/cannula as a projectile under normal operating conditions in disposable syringes, includes the said integral axial-mode ratchetlpawl mechanism, whereby the plurality of the said canti!evered pawls comprise a multiplicity of pawls distributed circumferentially but without the said flexible arm of the said shoe of the paw! and the said saw-teeth/notches of the shoe cut directly and within the entire length of the internal surface of the said collar, and where the shape-profile and the dimensions of the saw-teeth/notches of the pawl, including that of the saw-teeth/notches of the ratchet wheel, are optimised to achieve an easy one-way inward axial throughput of the common ratchet wheel with inhibition of its backward axial motion. a I...II. .S* p I *1 S * S S ** p S.IS I I..SSS