Background Art A shearing plant typically comprises a motor, the motor indirectly driving a driven shaft. The shearing plant, in use, is mounted at a point above a shearer's position, such that the driven shaft within a drive tube can extend downwardly for use by the shearer. The drive shaft and tube have provided at their end a hand- piece designed to be held by the shearer and used in shearing an animal, for example a sheep. The hand-piece is designed to convert the rotational drive from the drive shaft to a reciprocating motion that allows the wool or hair of the animal to be cut between a comb and a cutter provided at a leading edge of the hand- piece.

So as to facilitate the cutting of the hair or wool, both the comb and cutter are sharpened. Further, to allow the comb to enter the hair or wool of the animal its leading edge is also sharp. it is a problem experienced by shearers that if the hand-piece is dropped or otherwise out of the control of the shearer it can cut or injure either the shearer and/or the animal being shorn.

Whilst there are a number of potential causes for the hand-piece leaving the shearer's hand, the typical reason is the sudden locking or jamming of the comb and cutter of the hand-piece. This is often caused by the presence of a foreign object in the wool or hair of the animal. The inertia resulting from the blocking of the comb and cutter, effectively resulting from the reduction of the rotational speed of the drive shaft from 3500 rpm to 0 rpm, often forces the hand-piece from the shearer's hand.

Two forms of safety device are presently used with shearing plants, being a worm drive coupling and the safety clutch. The worm drive coupling is, a coupling used to attach the hand-piece to the drive shaft of the shearing plant. This coupling is typified by a broad male and female thread, the male thread being provided on the outer back half of the hand-piece. The male and female threads are designed in such a way that regular forward rotational drive from the drive shaft provides positive engagement in the coupling. However, a 180° turn in a reverse direction, of the hand-piece, will disengage the coupling. The arrangement of this coupling requires that the hand-piece be held very firmly by the shearer and the shearing plant effectively must be forced into reverse by 180° to fully disengage the coupling.

The second common safety device presently employed with shearing plants is a safety clutch. Typically, such a safety clutch comprises two drive blocks, effectively a dog clutch, which receive pressure from a spring provided therebetween. The pressure from the spring exerted on the drive blocks, when sufficient, allows drive to be transmitted through the clutch. The spring is adjusted to keep pressure on the drive blocks and transfer rotational drive. Unfortunately, once the clutch is forced to disengage a number of times, or the shearer adjusts the pressure on the spring, the performance of such a clutch is compromised. In many cases, a fast shearer may shear faster than the clutch allows, thereby the clutch disengages until the shearer slows down or adjust the clutch. As such, many shearers adjust the clutch so that it is effectively inoperable and no longer operates as a safety clutch.

Both present forms of safety device rely on the shearer's strong grip on the hand- piece. For example, each is effective if the grip is strong enough to either hold the hand-piece until it is turned 180° in reverse, or the safety clutch is forced to disengage. Further, in both such cases the shearing plant is still driving the drive shaft at 3500 rpm.

The applicants are aware of a further safety device, not commonly used, that only activates once a hand-piece is dropped by the shearer. However, such a situation

obviously interrupts the shearing process to a significant degree and may result in damage to the comb and cutter of the hand-piece.

The means for braking of the present invention has as one object thereof to overcome, or to at least provide a useful alternative to, the abovementioned problems associated with the prior art.

The preceding discussion of the background art is intended to facilitate an understanding of the present invention only. It should be appreciated that the discussion is not an acknowledgement or admission that any of the material referred to was part of the common general knowledge in Australia as at the priority date of the application.

Throughout the specification, unless the context requires otherwise, the word "comprise"or variations such as"comprises"or"comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

Disclosure of the Invention In accordance with the present invention there is provided a means for braking of an engine, characterised in that the means for braking comprises a sensor means arranged to detect the speed of revolution of a revolving component of or associated with the engine, the sensor means being in communication with a programmable logic controller whereby if the speed of revolution of the revolving component falls below a predetermined speed the engine is stopped.

In one form of the invention the revolving engine component is provided in the form of a drive pulley, the sensor means being positioned at a point adjacent to the drive pulley.

Preferably, the drive pulley has provided thereon a permanent magnet.

Still preferably, the sensor means is provided in the form of a response sensor.

The counting of the revolutions of the revolving engine component preferably does not begin until after a predetermined time has elapsed from start-up of the engine. This predetermined time may be, for example, 0.5 seconds after start-up.

Still preferably, the stopping time of the engine is minimised.

In accordance with the present invention there is further provided a shearing plant comprising a housing, a drive pulley, a driven pulley and a drive shaft used to transfer drive to a shearing hand piece, characterised in that a sensor means is provided to detect the speed of revolution of either pulley, the sensor being in communication with a programmable logic controller whereby. if the speed of revolution of either pulley falls below a predetermined speed the shearing plant is stopped.

Preferably, the sensor means comprises a response sensor provided adjacent the drive pulley.

Still preferably, a permanent magnet is provided on the drive pulley.

Brief Description of the Drawings The means for braking of the present invention will now be described, by way of example only, with reference to one embodiment thereof and the accompanying drawings, in which:- Figure 1 is a top plan view of a shearing plant in which is provided a means for braking in accordance with the present invention, the shearing plant being shown with an upper portion of the housing removed; and Figure 2 is a cross-sectional side view of the shearing plant of Figure 1.

Best Mode (s) for Carrying Out the Invention In Figures 1 and 2 there is shown a shearing plant 10 comprising a housing 12, a drive pulley 14, a driven pulley 16 and a belt 18 arranged therebetween.

The housing 12 comprises an upper portion 20, an intermediate portion 22 and a lower portion 24. The lower portion 24 of the housing 12 contains an electric motor 26. The electric motor 26 is arranged to drive the drive pulley 14. The driven pulley 16 is arranged to drive a drive shaft (not shown) that projects downwardly from the housing 12 and acts to transfer rotational drive to a shearing hand-piece (not shown).

A means for braking 30 is provided within the housing 12 of the shearing plant 10.

The means for braking 30 comprises a sensor means, for example a response sensor 32, a permanent magnet 34 and a programmable logic controller or a control integrated circuit (IC) 36, best seen in Figure 1.

The sensor 32 is mounted on a floor of an intermediate portion 22 of the housing 12, extending at least partially under the drive pulley 14 best seen in Figure 2.

The drive pulley 14 has the permanent magnet 34 positioned within a base thereof such that during revolution of the drive pulley 14 the permanent magnet 34 passes over at least a portion of the sensor 32. The sensor 32 is connected electrically to the control IC 36. The control IC 36 is programmed in a manner such that 0.5 seconds after start-up of the electric motor 26 of the shearing plant 10 the interval between impulses from the sensor 32 is monitored. The control IC 36 has a reference time programmed thereinto such that if the reference time is exceeded the electric motor 26 is brought to an immediate standstill. The switch- off time of a relay arranged between the control IC 36 and the electric motor is minimised utilising a special circuit, thereby allowing the electric motor 26 to stop as quickly as possible.

In use, a shearer (not shown) will operate a pull cord (not shown) which starts the electric motor. 0.5 seconds after the electric motor 26 is started the sensor 32 effectively begins counting the revolutions of the permanent magnet 34 provided in the drive pulley 14. The sensor 32 passes impulses imparted by the permanent magnet 34 to the control IC 36.

The drive pulley 14 passes rotational drive to the driven pulley 16 by way of the belt 18. The rotational drive from the driven pulley 16 is transferred to a shearing

hand-piece (not shown) by way of a drive shaft (not shown). Should the hand- piece jam such that the cutter either slows appreciably or locks entirely with respect to the comb, and the hand piece is held firmly by the shearer, the speed of rotation of the drive shaft, the driven pulley 16 and the drive pulley 14 will, in turn, be reduced. Once the rotation of the drive pulley 14 slows below a predetermined rate the control IC 36 causes the motor 26 to stop as quickly as possible, thereby preventing any injury to the shearer and/or the animal being shorn, and generally without the hand-piece leaving the shearer's hand.

The motor 26 provides drive at 2880 rpm. This rate of revolution is geared up to 3500 rpm in the drive pulley 14. The predetermined rate, below which the revolutions of the drive pulley 14 cannot pass without the motor 26 being stopped, is about 2700 rpm. However, it is to be understood that this target or trigger revolution figure may be varied without departing from the scope of the present invention.

It is envisaged that the sensor 32 may be arranged to monitor the rotation of other components of the shearing plant 10, for example the driven pulley 16.

It is further envisaged that the means for braking of the present invention may be applied to other devices containing rotational parts, including, for example, augers and mulching machines, both of which are known to cause severe injury due to the lack of appropriate safety devices. Still further, the pulleys described hereinabove may also be toothed wheels or cogs, or other arrangements/mechanisms by which drive may be transferred.

Modifications and variations such as would be apparent to the skilled addressee are considered to fall within the scope of the present invention.