WO1993003860A1

WO1993003860A1 - Dose dispensing gun

Info

Publication number: WO1993003860A1
Application number: PCT/AU1992/000452
Authority: WO
Inventors: Philip Bunce
Original assignee: Portland Surgical Products Pty Ltd; Enzacor Pty Ltd
Current assignee: Portland Surgical Products Pty Ltd; Enzacor Pty Ltd
Priority date: 1991-08-27
Filing date: 1992-08-27
Publication date: 1993-03-04
Anticipated expiration: 1994-02-27

Abstract

A gun dispensing doses of a veterinary or pharmaceutical product from a cartridge uses a bayonet-type mounting (16) for the cartridge in a housing at the forward end of the gun. The housing includes ribs (18) which bite into a rear end edge of the cartridge to ensure the cartridge is tightly held within the housing. Product is dispensed from the cartridge by means of a plunger (14) actuated by a trigger (26) via a ratchet mechanism. The primary components of the gun, including the ratchet mechanism, are made from a plastics material and means are provided for preventing the ratchet teeth from being stripped by repeated actuation of the trigger when the plunger has reached the limit of its movement.

Description

DOSE DISPENSING GUN

The present invention relates to a gun for dispensing doses of a fluid substance such as a veterinary or pharmaceutical product.

Certain veterinary and pharmaceutical products can be dispensed in measured doses in fluid form from a cartridge. In particular there have been proposed a number of veterinary products for oral administration to pigs, sheep, cattle, horses and other animals, with the product being of viscous or gel-like form.

A requirement exists for a gun for use with a cartridge containing a product in fluid form for dispensing discrete doses of the product.

According to one aspect of the present invention there is provided a gun for dispensing discrete doses of a fluid product from a cartridge associated with the gun, said gun comprising a plunger head engageable with a piston of the cartridge, and a trigger mechanism for advancing the plunger head in steps whereby to cause corresponding displacement of the cartridge piston and to thereby cause dispensing of a dose of the product, wherein the gun body includes a housing at its front end to releasably receive the cartridge, means for releasably retaining the cartridge within the housing, and means within the base of the housing and operative to bite into a rear end edge of a body of the cartridge whereby the cartridge can be firmly anchored between the base of the housing and the retaining means.

Advantageously, the retaining means comprises slots in the housing adapted to cooperate with projections on the cartridge body whereby to provide a bayonet-type fitting of the cartridge within the housing. According to another aspect of the invention there is provided a gun for dispensing discrete doses of a fluid product from a cartridge associated with the gun, said gun comprising a plunger head engageable with a piston of the cartridge, and a trigger for advancing the plunger head in steps whereby to cause corresponding displacement of the cartridge piston and to thereby cause dispensing of a dose of the product, wherein the plunger head is carried by a plunger rod and the trigger is linked to a plunger rod by a ratchet mechanism, the gun further comprising means defining a forward stop to limit forward advance of the plunger rod, and means for providing a rearwards resilient bias to the plunger rod when in its forward stop position whereby to prevent stripping of teeth of the ratchet mechanism by continued actuation of the trigger.

Advantageously, the stop is carried by the plunger rod and is resiliently deformable upon engagement with a rearwardly-directed abutment on a body of the gun.

An embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which:-

Figure 1 is an exploded view of a gun in accordance with the preferred embodiment of the invention;

Figure la is a fragmentary section through a cartridge-receiving housing at a forward end of the gun; Figure 2 is an exploded view of a cartridge for use with the gun;

Figure 3a is a schematic side view showing the rear end of the gun; and

Figure 3b is a side view similar to Figure 3a, but showing the configuration when a plunger rod of the gun is in a forward stop position.

As shown in the accompanying drawings a gun in accordance with the preferred embodiment of the invention comprises a body 2 having at its forward end portion a forwardly-opening housing 4 for receiving a cartridge containing product to be dispensed. As shown in Figure 2, the cartridge itself comprises a cylindrical body 6 of a plastics material with a dispensing nozzle 8 at its forward end and a piston 10 displaceable along the body 6 to discharge product through the nozzle 8. The body 10 is open at its rear end to permit the piston 6 to be engaged by a plunger 12 at the forward end of a plunger rod 14 of the gun to advance the piston 10 in discrete steps within the cartridge body 6. The detailed construction of the cartridge may be as described in our co-pending Australian patent application 89919/91.

The housing 4 releasably mounts the cartridge by a bayonet-type fitting.

For this purpose the wall of the housing is formed with opposed arcuate apertures 16 which communicate with the forward end of the housing via longitudinal grooves 18 whereby lugs 20 on diametrically opposed sides of the cartridge body 6 can engage within the grooves 18 upon rearwards movement of the cartridge axially into the housing 4 to then engage within the apertures 16 by rotational movement of the cartridge. The base of the housing 4 includes one or more forwardly projecting ribs 24 (Figure la) extending across the width of the housing and which, when the cartridge is rotated into position, bite at different points into a chamfered rear end edge 6a of the cartridge body 6 to ensure that the cartridge is held very firmly between the base of the housing 4 and the apertures 16 in the wall of the housing. The plunger rod 14 is mounted for axial movement within the gun body and carries at its forward end the head 12 which can be advanced by stepwise movement of the plunger rod 14 from a rear position adjacent the base of the housing 4 to a forward stop position which will be reached when substantially the entire contents of the cartridge have been dispensed. Advance of the plunger rod 14 is effected by means of a trigger 26 mounted within a handle 2a of the gun body and cooperating with the rod 14 through a ratchet and pawl mechanism to cause advance of the rod through a discrete step at each actuation of the trigger 26. The trigger 26 is pivotally mounted on a pivot 28 adjacent its upper end and is biased by a spring 30 to a forward position. A first pawl 32 is pivotally attached to the trigger 26 beyond its pivot point 28 so as to be advanced forwardly when the trigger 26 is moved rearwardly into the handle 2a. The pawl 32 is spring-biased into engagement with the teeth of a ratchet 34 formed along the underside of the plunger rod 14 in order to cause advance of the plunger rod 14. A second pawl 36 mounted within the body behind the first pawl 32 is spring-biased into engagement with the ratchet teeth to hold the plunger rod 14 against retraction when the trigger 26 has been released and the first pawl 32 is displaced rearwardly in preparation for the next stroke.

The stroke length of the first pawl 32 and hence the dosage achieved at each actuation can be controlled by means of a variable stop 38 positioned forwardly of the pawl 32. The variable stop 38 is in the form of a slide member displaceable laterally to present a selected one of a plurality of rearwardly-directed stop surfaces of different depth in front of the pawl in order to provide a variable forward stop position for the pawl 32. Alternatively, a similar effect can be achieved by providing a variable rear stop position for the trigger 26 to control the stroke length by controlling the maximum depression of the trigger 26 into the handle 2a. The variable stop for the trigger may comprise a cam 40 mounted on a wheel 42 within the trigger and engageable with an abutment 44 forming a fixed rear stop within the handle itself. Although for the purposes of illustration the gun is shown with both the slide 38 and the cam stop 40, in practice only one or other of these dosage controlling means will be provided. The slide 38 is satisfactory when only a single adjustment in dosage is necessary whereby one or other of the dosage rates can be achieved with the slide in one of two end stop positions, whereas the cam 40 is more suitable when a greater number of adjustment steps is to be provided.

As shown in Figure 3a the plunger rod 14 projects from the rear of the gun body and carries at its rear end a knob 46. The plunger rod 14 is reset into its rear position after reaching the forward end of its stroke, by rotating the knob 46 and thereby the plunger rod to disengage the ratchet teeth from the pawls 32, 36 whereby the rod 14 can be withdrawn to its rear stop position, the rod then being rotated to re-engage the pawls with the ratchet teeth in preparation for a fresh cartridge. In transverse section, the ratchet is concave and the pawls are convex in order to provide a stable rotational position for the ratchet in engagement with the pawls. The knob 46 also acts as a forward stop for the plunger rod 14 by abutment against the rear of the gun body. The forward stop provided by the knob 46 is constructed as a resilient stop which applies a rearwardly-acting bias to the plunger rod 14 when in its forward stop position. This rearwardly-acting bias tends to cause slight retraction of the plunger rod when the trigger 26 is released and prevents a user from stripping the pawl or ratchet teeth by actuating the trigger 26 when the plunger rod is in its forward stop position. In the embodiment shown, the necessary resilience of the stop is formed by constructing the forward face of the knob 46 as a resilient annular flange 46a which engages a projecting rib 48 at the rear end of the gun body, rearwards deflection of the flange 46a upon engagement with the rib 48 being restricted by means of a rigid part of the knob 46 spaced from and behind the resilient flange 46a. This action is illustrated in Figure 3b. In an alternative configuration, the rib 48 may be resiliently deflectable to provide the rearwards bias to the plunger rod 14 when in its forward stop position.

The plunger rod 14, including the forward head 12, the ratchet 34 and the stop-forming knob 46 at the rear may be integrally moulded from a suitable plastics. The gun body 2, the trigger 26 and the pawls 32, 36 may also be moulded from plastics, the biasing springs which bias the pawls 32, 36 into engagement with the ratchet teeth preferably being integral parts of the pawls themselves.

The above embodiment has been described by way of example only and modifications are possible within the scope of the invention.

Claims

CLAIMS.-

1. A gun for dispensing discrete doses of a fluid product from a cartridge associated with the gun, said gun comprising a plunger head engageable with a piston of the cartridge, and a trigger mechanism for advancing the plunger head in steps whereby to cause corresponding displacement of the cartridge piston and to thereby cause dispensing of a dose of the product, wherein the gun body includes a housing at its front end to releasably receive the cartridge, means for releasably retaining the cartridge within the housing, and means within the base of the housing and operative to bite into a rear end edge of a body of the cartridge whereby the cartridge can be firmly anchored between the base of the housing and the retaining means.

2. A gun according to claim 1, wherein the retaining means comprises slots in the housing, said slots opening to the front of the housing and being adapted to cooperate with projections on the cartridge body whereby to provide a bayonet-type fitting of the cartridge within the housing.

3. A gun according to claim 1 or claim 2, wherein the means for biting into the rear end edge of the cartridge body comprises at least one rib extending forwardly from the base of the housing.

4. A gun according to claim 3, wherein the or each said rib extends across the housing whereby to bite into the rear end edge of the cartridge at two spaced positions.

5. A gun according to any one of claims 1 to 4, wherein the plunger head is carried by a plunger rod and the trigger is linked to a plunger rod by a ratchet mechanism, the gun further comprising means defining a forward stop to limit forward advance of the plunger rod, and means for providing a rearwards resilient bias to the plimger rod when in its forward stop position whereby to prevent stripping of teeth of the ratchet mechanism by continued actuation of the trigger.

6. A gun according to claim 5, wherein the stop is carried by the plimger rod and is engageable with a rearwardly-facing abutment on a body of the gun, one from said stop and abutment being resiliently deformable upon engagement whereby to provide said resilient bias to the plunger rod.

7. A gun for dispensing discrete doses of a fluid product from a cartridge associated with the gun, said gun comprising a plunger head engageable with a piston of the cartridge, and a trigger for advancing the plunger head in steps whereby to cause corresponding displacement of the cartridge piston and to thereby cause dispensing of a dose of the product, wherein the plunger head is carried by a plunger rod and the trigger is linked to a plunger rod by a ratchet mechanism, the gun further comprising means defining a forward stop to limit forward advance of the plunger rod, and means for providing a rearwards resilient bias to the plunger rod when in its forward stop position whereby to prevent stripping of teeth of the ratchet mechanism by continued actuation of the trigger.

8. A gun according to claim 7, wherein the stop is carried by the plunger rod and is engageable with a rearwardly-facing abutment on a body of the gun, one from said stop and abutment being resiliently deformable upon engagement whereby to provide said resilient bias to the plunger rod.

9. A gun according to claim 8, wherein the stop is formed by a resilient flange at a rear end of the plunger rod, said flange being rearwardly deflectable through a limited distance on engagement with the abutment.

10. A gun according to claim 9, wherein the flange forms part of a knob at the rear end of the plunger rod, said knob permitting the plunger to be rotated out of engagement with the ratchet mechanism whereby the plunger rod can then be withdrawn rearwardly.