BACKGROUND ART It is common for tractors and other vehicles to have a power-take-off driveshaft so that various implements can be attached to the driveshaft, thereby making the vehicle able to perform a variety of agricultural tasks. Attached implements include augers, rotary hoes, slashers and a myriad of other such implements which are towed behind, or supported by the tractor. These implements are powered by the tractor via the PTO driveshaft.

The tractor, etc, typically contains a rear PTO outlet which usually comprises a relatively short rotating shaft (typically about 20 centimetres long) which is fitted with some form of coupling to enable a much longer rotating driveshaft to be fitted to the short shaft. Various devices (e. g. augers) can then be powered by the longer rotating driveshaft. The longer rotating driveshaft typically has a length of between 1-4 metres, and a diameter of between 50-300 millimetres. The shafts are typically made of steel, or strong plastic.

The power is transmitted directly from the engine and in the case of a tractor it can deliver between 20-150 horsepower (hp). Machines are usually designed for the PTO to run at 540 revolutions per minute (rpm) or 1000 rpm (although this can vary). To enable the various implements to be quickly attached to the power takeoff driveshaft, the driveshaft is exposed. However, this creates a potential safety hazard.

One difficulty is that the relatively long power takeoff driveshaft is also positioned in amongst the hydraulic lifting arms. Therefore, when the farmer attaches and releases implements to or from the hydraulic lifting arms the farmer will be in proximity of the power takeoff driveshaft. There have been many injuries and deaths caused by a person becoming caught on the exposed rotating driveshaft.

Various attempts have been made to improve the safety to the farmer when attaching or releasing implements from around the power takeoff driveshaft.

One known system uses a kill switch in the tractor which turns off the driveshaft. The main disadvantage with this system is that if the farmer is behind the tractor and inadvertently gets caught in the power takeoff driveshaft, there is little use in having a kill switch in the tractor cabin. Sometimes, some form of kill switch is provided in the power takeoff area, but should the farmer become caught and panic, the death or injury can result before the kill switch is activated, for the kill switch may not be within arms reach of the farmer.

It is known to provide some form of safety system which is attached to the implement (e. g. slasher) which is connected to the lifting arms and the power takeoff. However, the main disadvantage with this system is that it is attached to the implement which means that every implement must have its own safety system (which is expensive, difficult to maintain and repair) or the safety system must be separately attached to the implement every time the implement is attached to the tractor. This creates a number of additional disadvantages including improper positioning of the safety system or even failing to attach a safety system.

It is also known to provide safety shields which extend about the power takeoff area, but these are relatively clumsy and in the way.

It also seems to be known to provide motion sensors, infrared sensors and the like to detect movement, but these need to be positioned very accurately, and are frequently damaged, and are not very reliable as they can become covered or caked in dirt, dust, crop residue, etc.

Therefore, there would be an advantage if it were possible to provide a reliable and effective safety system that can be fitted to the tractor (or other prime mover) and which does not require the farmer to press a button or activate a lever to switch off the power takeoff if accidentally caught. There would also be an advantage if such a safety system would not unnecessarily interfere with an existing driveshaft.

OBJECT OF THE INVENTION It is an object of the invention to provide a safety device which may at least partially overcome the above-mentioned disadvantages or provide the consumer with the useful or commercial choice.

It is a preferred object of the invention to provide a safety device for shutting off the power to a power-take-off driveshaft in an emergency situation.

SUMMARY OF THE INVENTION According to a first broad form of the invention, there is provided a safety system for limiting power to a power-take-off driveshaft comprising: at least one detector for sensing the presence of an obstruction to the driveshaft ; and cut-off means for limiting power to the power-take-off driveshaft upon activation of the detector by the obstruction.

The sensing of an obstruction by the detector can activate the detector to signal the cut-off means to affect a reduction in speed or complete loss of power to the power-take-off driveshaft.

Power-take-off driveshafts are typically used to allow power to be transmitted through a shaft from another source, typically from a vehicle or a stationary motor. The typical vehicles used in agriculture would include tractors, commercial vehicles such as utilities and four wheel drives, but any type of vehicle with a power-take-off driveshaft, could be protected by the safety device.

The driveshaft may have a length of between 1-6 metres and will typically have a length of between 1-3 metres. The driveshaft may have a diameter of between 50-400 millimetres. The driveshaft will typically comprise a tubular member and may comprise a metal tubular member. The driveshaft may comprise a plurality of smaller shaft members that are attached together. It is not considered that any particular limitation should be placed on the present invention by any unnecessarily narrow definition of the term"driveshaft". It is considered that this term should include any member or means to transfer power from the tractor/vehicle to an appliance and which is of a design or configuration that can injure a user should the user touch or become entangled with the driveshaft.

The detector will preferably comprise a line member. The line member will preferably comprise a flexible but substantially inextensible line member (that is a flexible line member that does not unduly stretch). The line member may therefore comprise a wire, a rope, a cable, a chain, a strap, a band, a combination of these, and the like. The line member may be made of metal, plastic, composite materials and the like. It is not considered that any unnecessarily limiting scope should be placed on the term the line member. If desired, a plurality of line members may be provided and these may be attached to each other, separate to each other and the like.

The function of the line member will be to facilitate a power cut-off should a person become entangled with the takeoff shaft. Therefore, it is envisaged that the line member will extend substantially along the length of the shaft. However, if there is little likelihood of injury along some parts of the shaft, it is envisaged that the line member may extend only along the parts of the shaft where the risk of injury is real.

It is envisaged that for larger or more complicated shafts, it may be necessary to provide more than one line member. Thus, it is envisaged that a plurality of line members may be provided extending along at least part of the length of the shaft, and it is envisaged that this will be substantially equally spaced apart if desirable.

An obstruction will generally be a person or a large object which interferes with the operation of the power-take-off driveshaft, or is damaged by or causes damage to an implement attached to the driveshaft.

The presence of the obstruction could be within a specified proximity to the power-take-off driveshaft an attached implement, a particular weight contacting the surface of the shaft, or an object interfering with the operation of the driving of the shaft or other detectable events..

Sensing refers to any control means used to identify when an event has occurred, in this case the presence of an obstruction. An event which meets prerequisite conditions (for instance as set by the sensitivity of the device), is reported back to the detector by a control loop. This can be in the form of continuous signals which are interrupted or the transmission of a single signal upon conditions being met or the occurrence of a mechanical event.

Due to the rugged environment envisaged for use of this safety device, it is important that the sensitivity of the detector can be adjusted so that the device does not limit operation due to minor events such as the presence of a blade of grass.

The sensitivity should be suitable to pick up the presence of a small child too proximate to the driveshaft. Less rugged environments will call for a more sensitive setting of the detector.

Activation of the detector occurs when the detector senses the presence of the obstruction at the power-take-off driveshaft and signals the cut-off means to activate. For example when a person or other large object comes too close to, is too

heavy or slows rotation of the power-take-off driveshaft, the detector senses this obstruction and the cut-off means is activated. Ideally the detector will be located on or near the power-take-off driveshaft.

Preferably, the cut-off means is a breakaway switch. When this switch is activated it creates a break in the circuit to divert charge away from the power-take- off driveshaft. It is envisaged that various different types of cut-off means may be provided that are activated by the line member. In one version, the cut-off means may comprise one part of a switch which is attached to or relative to the line member such that when the line member is pulled or tugged, the switch is activated to cut-off power. For example, the switch may comprise a simple pullout switch which cuts off power. Of course, no particular limitation should be placed on the invention merely by describing this type of switch as an example. It is considered that a skilled person would be able to develop other types of cut-off means that will fall in the scope of the present invention.

The cut-off means will typically reduce or completely cut power to the PTO or will typically reduce or completely stop rotation or operation of the shaft. It is considered that no particular limitation should be placed on the invention by the exact manner by which this occurs. For instance, the cut-off means may reduce or cut-off engine power to the tractor/vehicle. Alternatively, the cut-off means may deactivate the PTO or the shaft in some other way. For instance, some form of clutch may be provided which is activated to cut-off the power. Alternatively, some form of engaging member may be provided which engages with the PTO. Alternatively, some form of braking device may be provided to stop rotation of the shaft.

It is preferred that the cut-off means is positioned in such a manner that the line member is proximal to the driveshaft. Thus, there may be an advantage in having the cut-off means positioned relatively close to the PTO of the vehicle. For instance, the cut-off means could be mounted anywhere on a 360° radius of the power takeoff driveshaft and typically within 50-500 millimetres and preferably within 150 millimetres of the power takeoff driveshaft. An advantage of this arrangement is that the line member can be stretched between the cut-off means and adjacent the other end of the driveshaft.

The line member can be attached to or relative to the cut-off means by any suitable manner. Typically, the line member will be directly attached to the cut-

off means, or to part of the cut-off means. However, it is envisaged that the line member could also be indirectly connected to the cut-off means. It is also envisaged that the line member could be attached to a pulley, or other guide means to guide the line member to the cut-off means.

The line member may have one end attached to or relative to the cut-off means, and another end attached to or relative to the other end of the shaft. Typically, the other end of the line member will be attached to the device which is powered by the shaft. In any event, it is preferred that the line member is attached in such a manner that it is not too far away from the shaft. The line member may be spaced from the driveshaft by a spacing of between 5-400mm.

If the line member is attached to the device which is powered by the shaft, the device may adopt some movement relative to the shaft. For this reason, the line member may need to have some length adjustability in order to not trip every time the device adopts some movement relative to the shaft. In a simple form, the line member can be made somewhat longer, however the line member may then sag relative to the shaft and this may not be desirable. Alternatively, a spring or like member may be provided which keeps the line member relatively taut but still allows some length adjustment.

It is envisaged the device could limit power to the power-take-off driveshaft by governing or regulating the speed of the engine, or in extreme cases totally cutting power to the driveshaft. This could be affected by the inclusion of various mechanical or electrical means to reduce the speed of the engine.

A particularly attractive advantage of the device is that the engine will not run or will stall if running, when the breakaway switch is not connected when the power-take-off driveshaft is engaged. Thus the device will ensure the breakaway switch is operational before power is supplied to the power-take-off driveshaft.

Another advantage of the device is it can be used on any power-take- off driven equipment, to improve safety.

In order to increase the safety aspects of the present invention, it is envisaged that some form of alarm will be activated should the cut-off means be activated. The alarm may be a visual alarm for instance a flashing light, or an audio alarm. It is also envisaged that some form of signal can be sent remotely should the safety device be activated and not be switched off within a suitable period of time.

The signal may comprise part of an EPIRB device, or any other type of signalling device that can summon emergency help should the safety device be activated and not switched off within a suitable period of time (typically 1-15 minutes). It is also considered that a completely separate manual cut-off switch may be provided as well as the safety device as described above.

BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the invention will be described with reference to the following illustrations in which: Figure 1. Illustrates the rear of a tractor containing a power takeoff shaft which powers a ground auger and where the shaft is protected by a line member which comprises part of the safety device of the present invention.

Figure 2. Illustrates the cut-off switch positioned adjacent the PTO of the tractor according to one embodiment.

Figure 3. Illustrates the same cut-off switch of figure 2 from a different angle.

Figure 4. Illustrates the cut-off switch according to a second embodiment.

Figure 5. Illustrates the cut-off switch according to a second embodiment.

BEST MODE Referring to the illustrations and initially to figures 1-3, there is illustrated a tractor 10 having a conventional PTO 11 (best illustrated in figure 2).

The PTO 11 comprises a short rotating shaft 12 terminating in a coupling 13 (typically a universal joint). This arrangement is well-known.

In the particular embodiment, a ground auger assembly is supported by the rear of the tractor. The ground auger assembly comprises a gearbox 14 which drives auger 15. A support frame 16 supports gearbox 14 and is attached to the lifting and lowering linkages on the rear of tractor 10 as is conventional.

The gearbox 14 is driven by a driveshaft 17. Driveshaft 17 couples to coupling 13 on the PTO at one end, and couples to a coupling 18 on gearbox 14 at the other end. The driveshaft 17 can be quite long and will typically have a length of between 1-3 metres. The driveshaft 17 rotates about its longitudinal axis and can have a rotational speed of between 500-1000 rpm. In the particular embodiment, rubber protection boots 19 are fitted about the coupling at each end of driveshaft 17.

It can be seen that driveshaft 17 provides a danger to a nearby operator.

For instance, the operators clothing can become attached to the driveshaft and,

because the driveshaft rotates, the operator can become severely injured.

To prevent this, a safety line member is provided. The line member in the particular embodiment comprises a plastic coated wire rope 20. One end of line member 20 is attached to a cut-off switch 21 best illustrated in figure 2 and figure 3 and which will be described in greater detail below. The other end of line member 20 is attached to the particular device being operated by driveshaft 17, and in this particular embodiment, the other end 22 of line member 20 is attached to gearbox 14.

The length of the line member is such that it is spaced from, but not too far away from driveshaft 17 (e. g. between 50-300 millimetres from the driveshaft).

Rotation of driveshaft 17 will not interfere with the line member 20.

The"gearbox"end 22 of line member 20, in this precise embodiment, is attached in a particular manner to accommodate movement between the gearbox and driveshaft 17. This movement is caused by coupling 18 being a"universal joint" type coupling which means that gearbox 14 can move sideways and up and down relative to driveshaft 17 by a small distance. In order to prevent this type of movement from triggering the line member, the line member is made a bit longer.

However, to prevent the line member from sagging too far away from driveshaft 17, a spring 23 is provided. One end of spring 23 is attached to line member 20 about 20- 60 centimetres away from where the line member is attached to the gearbox, and the other end of spring 23 is attached to the gearbox. The spring keeps line member 20 where it should be which is alongside, and somewhat above driveshaft 17.

The other end of line member 20, as mentioned before, is attached to the cut-off switch 21. Cut-off switch 21 in the particular embodiment comprises two housing components being a main housing component 24 which is attached to tractor 10, and a pull off component 25. Component 25 can be seen as a pull off cap, which is attached to main housing component 24 using a"press fit"arrangement or any other type of arrangement that allows component 25 to be pulled off component 24 but only if line member 20 is given a substantial tug. Inside cut-off switch 25 is a switch member (not illustrated) which is activated when pull off component 25 is removed from main housing component 24. This can occur if a person pulls line member 20, or if a person becomes entangled on shaft 17. To explain, if a person becomes entangled on shaft 17, the line member 20 will be pulled about driveshaft 17 and this will cause the line member to pull off component 25 to activate the cut-off

mechanism.

The cut-off switch 21 then sends a signal to any suitable part of the tractor electrics, electronics or mechanical components to switch off the PTO. For instance, the cut-off switch may comprise a breakaway switch which is normally open until activated. When activated, the breakaway switch supplies power to the tractor's shut down device (generally a solenoid on diesel tractors or a spark on petrol driven tractors). The shut down device limits power being supplied to the power-take-off driveshaft 17, so that the power-take-off driveshaft 17 reduces speed or stops rotating and the obstruction can be removed. The breakaway switch receives power when a second switch on the power-take-off engagement lever activates a relay to complete the circuit.

The safety device is usually attached to the solenoid of diesel engine tractors or the sparks of petrol engine tractors. For earlier model diesel engines (without a shutdown solenoid) a solenoid is fitted to an injector pump with a split link so as not to interfere with the manual stop. On petrol engine tractors, the breakaway switch activates a relay which earths the ignition system thereby shutting down the engine.

The circuit can also be in reverse polarity with power always to the shut down device (for instance the solenoid) and switches to interrupt the power.

In the particular embodiment, a manual"off'switch 26 is provided on the rear of the tractor which can also switch off the PTO under non-emergency conditions.

Typically, an alarm will sound if the cut-off switch is activated. The alarm will sound for a suitable period of time (typically 1-10 minutes) to warn adjacent people, but can also be used to awaken an injured and/or unconscious worker. A visual alarm such as a flashing light may also be used.

In a more sophisticated version of the invention, it will be possible to fit an EPIRB (emergency position indicating radio beacon) which will be activated upon tripping of the line member 20. However, the device will not be activated for a period of time (typically 5-20 minutes) to enable the safety device to be reset in case the line member has tripped by accident, or has tripped without an injury having been sustained. In the event of a serious injury, the device will send a signal to rescue personnel. It is envisaged that this version of the invention will find popularity in remote areas. Of course, devices other than an EPIRB could be used including a

satellite phone system, a digital system, an analogue system and the like.

Figures 4 and 5 illustrate a slightly different embodiment where the cut-off switch 21 is of a slightly different design and contains a pullout pin 28 which is attached to line member 28 and otherwise works in a similar manner to that described above.

It would be understood by a person skilled in the art that there are many ways to detect the presence of an obstruction for example by measuring interruption to beams, detecting excessive forces or detecting changes in acceleration of the power- take-off driveshaft. Thus transducers, accelerometers, piezoelectric sensors and other means could be used to detect the presence of an obstruction along the power-take-off driveshaft.

The term"comprise", or variations of the term such as"comprises"or "comprising", are used herein to denote the inclusion of a stated integer or stated integers but not to exclude any other integer or any other integers, unless in the context or usage an exclusive interpretation of the term is required.

Whilst the above has been given by way of illustrative example of the invention, many modifications and variations may be made thereto by persons skilled in the art without departing from the broad scope and ambit of the invention as herein set forth.