TECHNICAL FIELD OF THE INVENTION

This invention relates to safety equipment for use with motor driven saws, such as chain saws, clearing saws, circular saws, jig saws, band saws, and the like, all of which are herein collectively referred to as motor driven saws.

BACKGROUND OF THE INVENTION

Motorised saws suffer from a severe disadvantage in that the operator can inadvertently contact the rotating or moving saw blade, often suffering serious injury before the operation of the saw blade or chain can be stopped. This situation can occur whether the saw is fixed or portable and is regardless of the shape, structure or motion of the blade. Portable circular saws are generally fitted with a spring loaded guard, but the operation of the guard can become faulty and even when operating correctly, the guard might not provide adequate protection to the operator in certain circumstances.

Chain saws are particularly dangerous. This is because the cutting chain is guided around a support bar at a very high speed and the teeth are essentially unprotected. If the teeth should touch the operator while the saw is operating, this can result in severe lacerations. Such accidents happen to even highly experienced operators and result from a variety of reasons. One of the most accident prone happenings is the result of " kick¬ back" which occurs when the tip of the saw strikes an object which results in the saw being violently kicked backwards towards the operator. In an endeavour to minimise this hazardous situation, chain saws are equipped with a chain brake which is a mechanically

operated device and which is so constructed that in the event of a kick back, an operative part of the chain brake will lag behind the movement of the saw due to inertia and/or a part of the chain brake operating mechanism will contact the arm, wrist or hand of the operator. This will operate a brake on the clutch drum and also disconnect the drive from the chain saw motor to very rapidly bring the rotation of the chain saw on the bar to a complete halt.

While such a chain brake is generally highly effective in kick-back situations, it is of little help in other hazardous situations whereby through improper use or inadvertence, the teeth of the moving chain can come into contact with the operator's body.

The linear speed of a chain saw around the bar of the machine varies depending upon the size of the saw and other factors. A typical linear speed of a chain is in the region of between 20 and 30 metres a second which means to be effective a chain brake must operate within a small fraction of a second to obviate serious injury. Chain brakes currently available will, upon activation, enable a chain to come to a complete halt in something of the order of 50 to 100 thousandths of a second.

It will be apparent from the foregoing discussion, that although the invention is primarily concerned with providing a safety equipment for use with chain saws, nevertheless the field of the present invention is not intended to be restricted to chain saws since the inventive concept can be readily applied to a variety of cutting devices, such as those which utilise a saw blade which is rotated or otherwise operated by mechanical power. All of the known motor driven saws can therefore be incorporated with a braking mechanism which when operated in accordance with the teachings of this invention, will bring the operation of the saw to a halt substantially instantaneously.

OBJECT OF THE INVENTION

It is therefore an object of this invention to provide a means of detecting an impending contact between the saw blade and the operator and of triggering a braking device to halt die operation of a motor driven saw.

It is a yet further object of this invention to provide a means which will activate the mechanism of a chain brake of a chain saw to reduce the possibility of the teeth of a moving saw from coming into contact with the body of the operator or any other object

which is to be protected from injury by the chain saw.

SUMMARY OF THE INVENTION

Accordingly one form of the invention comprises a safety arrangement for a motor driven saw wherein means associated with the said saw are provided to emit an electromagnetic signal and to detect a reflection of the signal and upon said detection, to transmit an activating signal to activate a brake mechanism to halt operation of the said saw.

Preferably the electromagnetic signal comprises a beam of light and preferably at least one sensor is provided to detect a reflection of the said electromagnetic signal.

Preferably the sensor includes an filter to filter spurious electromagnetic signals.

Preferably at least two said sensors are positioned to detect a reflected electromagnetic signal.

Preferably the arrangement includes at least two means to emit an electromagnetic signal and at least two senso ^r s.

Preferably the arrangement includes a woven or non-woven fabric which incorporates means to reflect the said electromagnetic signal.

In another form, the invention comprises a safety arrangement for a motor driven saw and which includes detection means capable of detecting the proximity of a selected article to the saw and upon detection to transmit an activating signal to activate a brake mechanism to halt operation of the saw.

Preferably the selected article includes an electrically conductive element charged to emit the electromagnetic signal.

Preferably the detection means is capable of generating an activating signal consequent upon the detection means touching the said article.

Preferably the detection means is a proximity sensor adapted to detect the presence of the said article when the article approaches closer than a predetermined distance to the teeth of the saw.

Preferably the selected article is an article of clothing to be worn by the operator of the saw.

In yet another form the invention comprises a safety arrangement for a motor driven

saw wherein means are provided to detect the alteration of the status of an electrical circuit in an article to be detected and upon such detection to transmit an activating signal to activate a brake to halt operation of the saw.

Preferably the said article to be detected comprises a woven or non woven material which includes an electrically conductive member which forms part of an electrical circuit and preferably the means to detect the alteration of the status of the circuit will be activated upon the electrical circuit being interrupted.

Preferably the said article comprises an article of clothing to be worn by the operator of the saw.

Preferably the motor driven saw is a chain saw which includes a motor, a substantially rectangular saw bar having a major and a minor axis and having a periphery formed to receive and guide an endless saw chain, and a chain brake mechanism adapted upon activation to disconnect the said drive to the saw chain.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A preferred from of the invention will now be described with the aid of the accompanying drawings which is illustrative of one form of the invention, but which is not to be limited to the illustrated form.

Fig. 1 is a diagrammatic representation of a typical chain saw which incorporates one of the features of the present invention.

Fig. 2 is a diagrammatic representation of another form of the present invention.

The basis of the present invention is the utilization of a brake for the saw blade or saw chain which is activated by an electrical or electronic signal. This is arranged by utilising a means for generating the electrical or electronic signal whenever the saw blade or the chain of the saw approaches within a specified distance to an object to be protected or when an alteration in the status of an electrical circuit is detected and for this signal to trigger and so activate the chain brake.

In one preferred form, this object is achieved by incorporating a substance in, or by modifying the fabric that forms part or all of the clothing worn by the operator so that either the fabric or the material embodied or incorporated in the fabric, emits a signal which can be received by an electrical or electronic sensor which transmits a signal or initiates a signal which will activate the brake mechanism for the saw blade or the saw chain. In another form the fabric is modified or constructed so it will be capable of reflecting a signal directed at it, whether the signal be electromagnetic radiation or visible or invisible light. In yet another form, the signal source can consist of a metal thread or the like embedded in or otherwise attached to an article of clothing to be worn by the operator of the saw, with the metal thread being connected to a signal source.

The fabric can form part or all of the clothing of the operator or can be provided as an accessory to be worn by the operator in the positions desired to be protected.

The fabric may be provided with a reflective or retro-reflective surface which is capable of reflecting visible or invisible light or electro magnetic radiation. A retro-

reflective surface is a surface which is capable of reflecting at least a part of the signal back to the source of the signal. Various forms of fabric which exhibit the desired reflective and/or retro-reflective properties are known. One form of suitable fabric which can have the desired properties can be manufactured for instance by having a thread or threads woven into the fabric either during or after manufacture which will provide the required reflective capabilities. In another form the manufactured fabric can be treated so it will exhibit the required reflective or retro-reflective capability. In addition to the reflective and retro-reflective capabilities, the fabric can also be provided with other

characteristics such as resistance to tear, resistance to the penetration of moisture and so forth.

Fig. 1 illustrates diagrammatically one method of utilizing the reflective and/or retro-reflective properties of the fabric in conjunction with an electronic chain brake on a chain saw. In this Figure, the chain saw 1 incorporates the usual saw bar 2 and a chain with saw teeth 4. The chain saw which can be powered by an electric or petrol engine (not shown in the drawings) as is known in the art, includes the usual form of manually operable chain brake triggering mechanism as indicated at 3. In addition to the manually operable triggering mechanism 3, the chain saw also includes an electrically or electronically operated triggering mechanism which, when it receives a signal, will activate the chain saw brake mechanism. In this particular form of the invention, signal emitting devices 6 are provided which are capable of transmitting a signal indicated by the dashed lines 7 which when it impinges on the fabric will be reflected back to a sensor or sensors

(not shown in the drawings) located on the front of the housing of the chain saw. A suitable signal generator is provided to generate the signal which is emitted as a visible or non-visible beam.

Preferably two or more of the sensors are utilized in conjunction with signal emitting devices 6 which will emit an electromagnetic signal which may be a beam of light, either visible or invisible, which in one form may be directed substantially parallel to the major axis of the bar of the chain saw but spaced a short distance from the teeth of the chain such as that indicated by the dashed lines 7. Each sensor is programmed to generate a triggering signal only when it receives a reflected signal from the signal emitting device 6. A suitable electronic or electrical filter is preferably provided to minimise the sensor being triggered as a result of receiving false or spurious signals.

The construction is such that if any electromagnetic energy generated by the signal emitting devices is reflected back from the signal emitting device to any of the sensors associated with the saw, this will send an electrical or electronic signal to the means which activates the electronic brake.

Preferably as indicated in the drawing, both a signal emitting device and a sensor is positioned above and below the bar of the chain saw thereby ensuring that an object cannot touch the chain bar or come closer than a predetermined distance without first interrupting one or more of the beams. If the object interrupting the beam is of a retro- reflective nature then the beam will be reflected back to the sensor to activate the chain brake.

It will be apparent that apart from forming the clothing to be worn by the operator so that all or part of the surface of the clothing is composed of retro-reflective fabric it is also possible to cover any part of the human body or any other object to be protected and to protect that part simply by covering it with retro-reflective fabric.

In another form, the fabric can be woven during manufacture with an electrically conductive element, such as a wire. In this modification, the wire can be charged to emit a signal or the element can be such that a sensor means on the chain saw can detect the element either by direct contact or by a proximity sensor so that upon contact by a tooth of the saw with the element, or upon the saw approaching closer than a preset distance from the fabric, the sensor will receive a signal which will generate an electrical or electronic triggering signal which is transmitted to activate the saw brake.

Another embodiment of the invention may comprise forming the clothing which can be trousers, jackets or footwear in a manner that the proximity of the clothing to the saw blade or chain saw bar is determined by the sensors so that if the saw blade or the chain saw bar comes to within a predetermined distance of the user's clothing or footwear then the chain brake will be activated.

Other proximity detecting mechanisms that can be utilized for the purpose of the present invention comprises ultra-sound, capacitive sensor, a magnetic sensor, a coded radio signal or a metal detector.

In a yet further form of the invention particularly as illustrated in Fig. 2, a garment to be worn by the operator may be formed wholly or partly of material already known in the art and which consists of saw cut resistant material. Such material is generally formed into a garment such as chaps or a pair of trousers 20. An electrically conductive member for instance an electrically conductive wire 21, may be incorporated into the material such as by being woven as part of the material or separately threaded through the material. The electrically conductive material can be connected as part of an electrical circuit which is

associated with the electrical or electronic saw brake so that upon severance of the electrically conductive wire, the electrical circuit will be broken and the saw brake will be activated. Various means of connecting the electrically conductive member to the circuit of the saw brake can be utilised. In one embodiment and as illustrated in conjunction with a motorised chain saw, the electrically conductive wire 21 can be connected by a flexible insulated electrical cable arrangement 22 through a glove 23 or the like which can be worn by the operator. The glove is provided with suitable conductive pads 24 which can contact corresponding pads 25 on the handle 26 of the chain saw. Figure 2 illustrates the use of a glove 23, but it will be apparent that the electrical connection can be made by using a right or a left handed glove, or both. While the use of a glove is a convenient means for carrying the necessary electrical connections, it will be apparent that any other convenient means of making or breaking the electrical connection between the electrically conductive wire 21 and the saw brake activating mechanism can be utilized. In the embodiment illustrated, the chain saw will operate only when the handle 26 of the chain saw is gripped by the gloved hand of the operator and the electrical circuit through the electrically conductive wire 21 is intact. However it is to be understood that the circuitry can also be formed so that the chain brake is activated when an electrical circuit is made.

While it is to be preferred that the material into which the electrically conductive element is woven is formed of saw cut resistant material, it is to be understood that the choice of the material is dependent upon specific requirements and it will be apparent to the skilled reader that a large variety of materials can be employed which will be satisfactory.

In yet another form the saw blade or the chain saw bar is adapted to emit a signal

which is recognised by the clothing. For instance, the clothing can act as a metal detector and consequently the metal saw blade or chain saw bar will be detected when it is within a predetermined proximity to the clothing. In yet a still further form the material forming the clothing is arranged to emit a signal which is recognised by the saw blade or saw chain.

By reason of the combination of the means to detect a signal which is capable of activating the electronic saw brake, even if the embodiment is employed which requires the teeth of the saw to actually contact the fabric which may form part of the clothing of the

operator, because of the extremely quick activation and consequent operation of the saw brake, injury to the operator from the teeth of the saw should be reduced.

While the foregoing description relates to preferred embodiments of the invention it is to be understood that any amendments and alterations diat will become apparent to those skilled in the art are intended to be included within the description and within the scope of any patent to be granted on the application as defined in the appended claims.