BACKGROUND ART Many different types of fluid dispensers have been developed to allow controlled volumes of fluid to be dispensed or expressed as required. For example, drench guns are commonly used in agricultural applications to dispense set dosage volumes of fluid onto or into livestock. Vaccination syringes are also used in the same applications.

In general terms, these systems normally employ a pistol grip arrangement where the rear of the pistol grip is pivoted or pushed forward by a user to in turn drive an internal piston forward within a dispensing chamber of a gun. The movement of the piston will then force fluid out of a nozzle associated with an exit port of the dispensing chamber. The gun handle normally incorporates a spring arrangement which places a biasing force on the rear section of the pivoting grip to pull same back and hence return the piston into its original position while drawing fluid back into the interior of the gun from a reservoir.

A two part pivoting design is normally applied to implement such pistol grip actuator systems. The rear section of this grip is normally squeezed by a user to move forward an associated drive shaft linked to the piston in the interior of the drench gun. The rear or second part of the grip or handle is pivoted through a set span with each actuation of the dispenser gun.

In some instances it is also preferably to control or adjust the volume of fluid dispensed by the drench gun in a single actuation or operation. The volume of fluid dispensed can be controlled by adjusting the rest position of the piston within the gun and its associated drive shaft. To dispense only a small volume of fluid the piston at rest can be retained in a position close to or towards the nozzle and/or dispensing end of the gun. Conversely, to dispense a larger dose of fluid, the piston at rest can be retained back towards the pistol grip end of the gun. However, as those skilled in the art would appreciate, the linkage of the rear section or portion of the pistol grip to the piston's drive shaft will in turn vary the width or span of the pistol grip as the volume of fluid to be dispensed changes.

This characteristic of such devices is seen as a disadvantage by some users or operators. As the size or span of the pistol grip provided enlarges or decreases with dose size, an operator of the gun may not necessarily be provided with a comfortable grip. For example, operators with relatively small hands may find it difficult to use a gun with a wide grip span when a large dose is to be delivered.

Conversely, operators with relatively large hands may find it difficult or uncomfortable to use a gun with a relatively small grip span when small doses of a drenching fluid are to be dispensed.

In alternative forms of such types of dispensers, it is also possible to control the dosage of fluids dispensed though limiting the travel of the piston associated with such an actuating grip. The grip provided may have a standard or fixed default width to provide for an accurate operation of such dose control mechanisms. However, this default grip width may not necessarily fit all users' preferences.

An improved draft assembly for a drench gun or other similar fluid dispenser which addressed any or all of the above problems would be of advantage. In particular, an improved drive assembly which allowed the width of a pistol grip handle or actuator for a fluid dispenser to be adjusted without necessarily adjusting the volume of fluid dispensed in a single operation would be of advantage.

All references, including any patents or patent applications cited in this specification are hereby incorporated by reference. No admission is made that any reference constitutes prior art. The discussion of the references states what their authors assert, and the applicants reserve the right to challenge the accuracy and pertinency of the cited documents. It will be clearly understood that, although a number of prior art publications are referred to herein, this reference does not constitute an admission that any of these documents form part of the common general knowledge in the art, in New Zealand or in any other country.

It is acknowledged that the term'comprise'may, under varying jurisdictions, be attributed with either an exclusive or an inclusive meaning. For the purpose of this specification, and unless otherwise noted, the term'comprise'shall have an

inclusive meaning-i. e. that it will be taken to mean an inclusion of not only the listed components it directly references, but also other non-specified components or elements. This rationale will also be used when the term 'comprised'or'comprising'is used in relation to one or more steps in a method or process.

It is an object of the present invention to address the foregoing problems or at least to provide the public with a useful choice.

Further aspects and advantages of the present invention will become apparent from the ensuing description which is given by way of example only.

DISCLOSURE OF INVENTION According to one aspect of the present invention there is provided a drive assembly for a fluid dispenser, said fluid dispenser including a chamber in communication with a source of fluid, said dispenser also including a piston moveable within the chamber to dispense fluid from and draw fluid into said chamber, wherein the drive assembly includes a drive shaft linked to the dispenser piston, wherein movement of the drive shaft causes movement of the piston, and an actuation element operable by a user of the dispenser, said actuation element being associated with the drive shaft, whereby operation of the actuation element will cause movement of the drive shaft, and a span adjuster associated with the drive shaft and directly connected to the actuation element, said span adjuster being adapted to move with respect to the

drive shaft while being adapted to transfer force applied to the actuation element to the drive shaft.

According to a further aspect of the present invention there is provided a drive assembly for a fluid dispenser, said fluid dispenser including a chamber in communication with a source of fluid, said dispenser also including a piston moveable within the chamber to dispense fluid from and draw fluid into said chamber, wherein the drive assembly includes a drive shaft linked to the dispenser piston, wherein movement of the drive shaft causes movement of the piston, and an actuation element operable by a user of the dispenser, said actuation element being associated with the drive shaft, whereby operation of the actuation element will cause movement of the drive shaft, wherein the drive shaft includes at least one extendable section capable of selectively increasing the length of the drive shaft, where said at least one extendable section is directly connected to the actuation element.

The present invention is adapted to provide a drive assembly for a fluid dispenser. The drive assembly provided can be used by an operator of the fluid dispenser to actuate same and trigger the dispensing of fluid and also recharging or refilling a dispensing chamber.

Preferably a fluid dispenser with which the present invention is to be used may include a chamber in communication with a fluid source or reservoir in addition to a piston moveable within the interior of the chamber provided. The action of the piston moving within the dispenser chamber can be used to draw fluid into

and subsequently dispense fluid from the chamber through at least one inlet and at least one outlet port provided within the chamber.

Reference throughout this specification will also be made to a fluid dispenser with which the present invention is to be used being a drench gun. Drench guns provide or dispense set volumes of dosages of fluid when actuated through the use of a piston moving within a dispensing chamber. However, those skilled in the art should appreciate that other types of fluid dispensers may also be used in conjunction with the present invention and reference to drench guns only throughout this specification should in no way be seen as limiting. For example, in one alternative embodiment the present invention may also be implemented or used with a vaccinating syringe or other similar type of apparatus if required.

In a preferred embodiment, a drive assembly provided in accordance with the present invention may be linked to a piston within the interior of the drench gun involved. The drive shaft may be adapted to move relative to the main body or components of the drench gun to in turn move the piston and associated piston head located within the drench gun's main chamber. In a further preferred embodiment, the motion of the drive shaft may be constrained to a single dimension only to ensure that the drive shaft will only be used to push or pull the piston provided within the interior of the drench gun chamber. Reference throughout this specification will also be made to the drive shaft being driven into and out from the interior of the drench gun chamber when the drive assembly provided is actuated.

In a preferred embodiment the drive assembly provided includes an actuation element operable by a user. A user of the drench gun and associated drive

assembly may employ such an actuation element to cause or trigger movement of the drive shaft and hence trigger the actuation or operation of the drench gun involved.

In a preferred embodiment the actuation element provided may be linked to or associated with the drive shaft to transfer any force applied to the actuation element by an operator or user through to the drive shaft. In this way operation or actuation of the actuation element will move the drive shaft to in turn trigger the dispensing and refilling of fluid within the drench gun chamber.

In a preferred embodiment the actuation element provided may be formed or configured as a pistol grip actuation system similar to that already current in use with existing types of drench guns. These pistol grip actuation elements can employ a two part design with a free or end portion pivotably mounted to a first section directly fixed to the body of the drench gun provided. The pivoting, second or free end of the pistol grip may be squeezed or pushed towards the second portion of the grip where a linkage between the second portion and the drive shaft will force the drive shaft into the interior of the drench gun chamber.

Once a user releases pressure applied to the rear section of the grip handle, a return spring provided within same can apply a biasing force to return the second portion of the grip back to its original position and hence draw the end of the drive shaft out from the central interior sections of the dispenser chamber.

Reference throughout this specification will also be made to the drive assembly provided using a pivoting pistol grip type actuation element substantially as described above. However, those skilled in the art should appreciate that references to pistol grip actuators throughout this specification should in no way

be seen as limiting as other alternative forms or designs of actuation systems may also be used if required.

In a preferred embodiment, the grip actuator provided may be linked to the drive shaft through a span adjuster. A span adjuster may be used to transfer force applied to the pivoting or free end of the grip actuator through to the drive shaft to in turn move the drive shaft and actuate the drench gun involved. A span adjuster may be adapted to selectively increase the length of the shaft and hence the position at which the grip actuator is connected to the shaft.

This effective lengthening of the drive shaft may adjust or change the relative position of the grip actuators link to the drive shaft, without necessarily changing the rest position of the piston directly linked to one end of the drive shaft. This in turn will allow the width of the grip actuator to be adjusted without necessarily changing the volume of fluid to be dispensed by the drench gun in a single operation or actuation.

In a further preferred embodiment, a span adjuster may be implemented through an extendable or extension section provided in association with a drive shaft.

Such an extendable section may preferably adjust or modify the relative length of the drive shaft without necessarily changing the location of the end of the drive shaft within the interior of the dispensing chamber of the drench gun involved.

In a preferred embodiment, the drive assembly may include a single span adjuster formed through a single extendable section located at the free or exterior end of the drive shaft provided. This single extendable section may be directly linked to the pivoting free end of the grip actuator and may also have an

adjustable or moveable connection to the end of the drive shaft. This configuration of the span adjuster allows the effective length of the drive shaft to be increased or decreased from its end.

Reference throughout this specification will also be made to the drive assembly including a single span adjuster located at the free or exterior end of the drive shaft provided. However, those skilled in the art should appreciate that a span adjuster formed by an extendable section of the drive shaft may be located in the body of the drive shaft at any required position, and need not necessarily be located at the free end of the shaft. Furthermore, reference throughout this specification will also be made to a span adjuster being formed through an extendable section which projects out from the end of the drive shaft. However, again those skilled in the art should appreciate that other configurations or arrangements of span adjusters which is directly connected to the drive assembly's actuator and linked to the drive shaft may be used if required.

In a further preferred embodiment, a span adjuster may be formed from a hollow section with approximately the same cross section or profile as that of the drive shaft. This hollow section may be attached to the end of the drive shaft with a moveable or adjustable connection to in turn allow the effective length of the drive shaft to be adjusted. In a further preferred embodiment, the moveable or adjustable connection of the span extender may be provided through a thread formed into the mating surfaces of the end of the drive shaft and the span adjuster provided. In such an embodiment, the span adjuster may be threaded onto and down the end of the drive shaft to reduce the distance at which the span adjuster projects out from the end of the drive shaft to in turn reduce the effective length of the drive shaft. Conversely, the span adjuster may be rotated

or threaded in the opposite direction to increase the effectiveness of the drive shaft.

Reference throughout this specification will also be made to a span adjuster or extendable section of the drive shaft to be provided through an element threaded onto the free end of the drive shaft. However, those skilled in the art should appreciate that other configurations or implementations of the span adjuster may be provided and reference to the above only throughout this specification should in no way be seen as limiting. For example, in one alternative embodiment, a section of the drive shaft may telescope in or out on themselves to in turn adjust the effective length of the drive shaft if required.

The present invention may be used to adjust or modify the effective length of the drive shaft provided without necessarily adjusting the relative position of the main body of the drive shaft with respect to the fluid dispenser with which the present invention is to be used. This can in turn allow the effective width of an actuator grip used in conjunction with the present invention to be adjusted without necessarily adjusting the rest position of a piston linked to the drive shaft and hence the volume of fluid to be dispensed in a single operation of the dispenser involved.

This configuration of the present invention also allows a user to set a comfortable grip width suited to their own preferences, irrespective of the volume of fluid to be dispensed.

BRIEF DESCRIPTION OF DRAWINGS Further aspects of the present invention will become apparent from the following

description which is given by way of example only and with reference to the accompanying drawing in which: Figure 1 shows a side cross section view of elements of a drive assembly configured in accordance with a preferred embodiment and installed on or in a drench gun.

BEST MODES FOR CARRYING OUT THE INVENTION Figure 1 shows a side cross section view of elements of a drive assembly configured in accordance with a preferred embodiment and installed on or in a drench gun.

The drive assembly (1) provided is formed from or includes a two-part actuation element, a pivoting actuator grip element (2). The actuator grip (2) provided includes a first fixed portion (2a) directly connected to the body of the drench gun (not fully shown) with which the drive assembly is to be used. The actuator grip also includes a rear second or free portion (2b) pivotably connected at point (2c) to the first portion (2a). This configuration of the actuator grip (2) allows the user to squeeze the rear section (2b) towards the front portion (2a).

Incorporated within the rear section (2b) of the actuator grip is a return spring (3). This return spring is loaded when the grip is squeezed closed with the spring being used to biase or pivot the second portion to the grip back into the original position shown when the squeezing force applied by a user is released.

The drive assembly also includes a drive shaft (4) and a span adjuster (5) which is used to link or associate the drive shaft (4) to the grip actuator (2). The drive shaft (4) is linked at its opposite end (not fully shown) within the interior of the

drench gun to a piston used to drive fluid out of and pulled forward into a dispensing chamber of same.

The span adjuster (5) provides an extendable section to the drive shaft to extend its effective length outwards from the body of the drench gun if required.

The span adjuster (5) is fixed or directly connected to the rear section (2b) of the actuator grip (2). Conversely, a threaded screw connection is provided to link the span adjuster (5) to the end of the drive shaft (4). This threaded linking connection allows the relative position of the span adjuster (5) to be adjusted with respect to the end of the drive shaft (4) so as to change the effective length of the drive shaft without necessarily changing the position of the end of the drive shaft within the dispensing chamber of the drench gun.

This configuration of the drive assembly shown allows the span or width of the actuator grip (2) to be adjusted to suit the requirements of a user of a drench gun. By moving the span adjuster outwards away from the end of the drive shaft, this will pull the second portion (2b) of the grip actuator outwards and thereby increase the span of the grip. The opposite action will in turn reduce the span of the grip for users with smaller hands.

Aspects of the present invention have been described by way of example only and it should be appreciated that modifications and additions may be made thereto without departing from the scope thereof.