This invention relates particularly but not exclusively to a hand-held electrical or compressed-air power tool having a trigger handle that is used to apply power to the tool to perform its function. It will therefor be convenient to here-in-after describe the invention with reference to this example application. It is however to be clearly understood that the invention is capable of broader application. For example, the invention is not to be limited to electrical or compressed-air power tools.

The term tool is to be broadly interpreted in this specification and to include all types of hand held machines and firearms. A firearm might for example be in the form of a hand held pistol or revolver or a rifle.

BACKGROUND TO THE INVENTION Hand-held power tools are widely used in building and manufacturing environments. The quintessential or typical hand-held electrical power tool is an electrical drill. This tool typically comprises a body with a rotating or working head that is a chuck into which a drill bit is inserted and a trigger handle for applying power to an electric motor contained within the body that drives the working head. Typically the tool is held by a user holding the trigger handle in one hand and power is applied to the motor to drive the working head by squeezing a trigger mounted on the trigger handle.

The tool is operatively coupled to a power supply, eg an electrical mains power supply, or an internal battery pack.

With a simple electric drill for domestic use power can be applied to the motor driving the working head simply by coupling the electrical lead to a mains supply and then pressing or squeezing the trigger. There is no impediment or resistance to the operation or function of the tool and the power tool can be switched on by small children playing with the tool.

In addition a powerful tool could be turned on by a person not having sufficient strength to control the tool leading to a dangerous situation. There is nothing to resist or inhibit them doing this.

One prior art or known safety device of which the applicant is aware is a locking pin which is recessed within the handle member and locks the trigger to prevent the application of power to the tool. This has some benefit as a safety feature. However it is relatively simple and unsophisticated. It would not be that difficult for a child or an unsophisticated user to remove the pin from its aperture.

Further most reputable brands of power tools made around the world are designed and intended for right handed persons. They often have a safety feature in the form of a locking or release pin accessible from the left side of the body of the tool. The problem for a left handed operator is that they have to switch the tool to their right hand and then remove the safety pin. This is a less than ideal situation.

Other known locking mechanisms for locking the power trigger"on"or"off"are described in US Patent Nos. 4,879, 438 and 5,638, 945. These locking mechanisms are of the type that once the locking mechanism have been activated from the"lock off" state, the tool can be operated with relative ease.

The tool described in US Patent No. 5,638, 945 is operated by use of the index finger and thumb. Once the trigger mechanism (or lock) is moved from the locked off position, the tool can be readily turned on by depression of the trigger. A child could easily move the trigger mechanism (lock) from the locked off position then operate the tool.

US Patent No. 4,879, 438 describes a lock mechanism that is mounted within the power trigger of the tool. It can be activated with a first finger pressure to an on-mode

with the requirement of a second finger pressure to lock it in an on-mode. Like the earlier mentioned prior art, it can be easily operated by a child.

Clearly it would be advantageous if a more efficacious safety feature could be devised that resisted the function or operation of a power tool unless it was appropriately manned. It would also be particularly advantageous if the threshold hand and finger strength required to overcome or disarm the safety feature could be adjusted for different applications.

SUMMARY OF THE INVENTION According to one aspect the present invention consists in a trigger handle for the operation of a power tool, the handle comprising: a handle member mounted on a tool body; a power trigger mounted on said member which has to be depressed by the index finger of a user's hand to cause power to pass to the tool to energise the tool ; and a safety trigger adjacent to said power trigger which has to be depressed by at least one of the user's remaining fingers before it is possible for said power trigger to be used to energise the tool.

Preferably said handle further comprises a blocking means intermediate the safety trigger and the power trigger, that acts to block the power trigger from being depressed until the safety trigger has been fully depressed.

Preferably said blocking means may conveniently comprise a blocking element pivotally mounted on the member with surfaces configured to complement respectively said safety trigger and said power trigger.

Preferably said safety trigger comprises an isolation switch which is closed when safety trigger is fully depressed which then permits the power trigger to be operated when the power trigger is also depressed.

Preferably said power trigger comprises a power switch that is closed when the power trigger is depressed after said safety trigger switch is depressed.

Preferably said safety trigger has a certain resilience that has to be overcome for said safety trigger to be depressed. Preferably said resilience is provided by a resilient biasing means in the form of a spring.

Preferably said power trigger has a certain resilience that has to be overcome for said power trigger to be depressed. Preferably said resilience is provided by a resilient biasing means in the form of a spring.

Preferably said handle further comprises a locking means for locking the power trigger and the safety trigger in respectively the activated and release positions during operation of the tool.

Preferably said locking means comprises a release means for releasing or deactivating the locking means on demand by a user.

Preferably said release means disengages said locking means when pressure is applied to at least one of said power trigger and said safety trigger.

Preferably said locking means comprises a toggle switch mounted on the handle member, locking elements releasably engaging each of said triggers, and at least one mechanism for operatively coupling said toggle switch to said locking elements.

Preferably said at least one mechanism may be in the form of a linkage extending from said toggle switch element to the locking elements.

Preferably said locking elements have teeth for engaging teeth on the complementary surface of the triggers.

Preferably said toggle switch is manually pivotable between on and off positions and comprises biasing means for biasing the switch towards the off position but being capable of being manually moved to the on position manually by a user.

Preferably said power tool comprising a tool body, a working head on which an active tool component is mounted and performs work.

Preferably said power tool is any one of a drill, a jackhammer, a hand held cutting device or a fastening device.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT A power tool and trigger handle in accordance with the invention may manifest itself in a variety of forms. It will be convenient to here-in-after describe in detail a preferred embodiment of the invention with reference to the accompanying drawings.

The purpose of providing this detailed description is to instruct persons having an interest in the subject matter of the invention how to carry the invention into practical effect. At the same time it is to be clearly understood that the specific nature of this detailed description does not supersede the generality of the preceding broad description. In the drawings: FIG 1 is a schematic side view of a tool and trigger handle in accordance with one embodiment of the invention; FIG 2a is a schematic sectional side view of the handle shown in Fig 1, showing the safety trigger and blocking means when the tool is in a passive mode.

FIG 2b is a schematic sectional side view of the handle shown in Fig 1, showing the safety trigger and blocking means when the tool is in an active mode.

FIG 3a is an enlarged view of the safety trigger and blocking means detail shown in Fig 2a.

FIG 3b is an enlarged view of the safety trigger and blocking means detail shown in Fig 2b.

FIG 4 is an enlarged perspective of the block and spring forming the blocking means shown in Figs 3a and 3b.

FIG 5 is an exploded view of the block shown in Fig. 4.

FIG 6 is an enlarged view of the spring shown in Fig. 4.

FIG 7a is a schematic side view of the handle shown in Fig 1, showing the locking means and lock release means when the locking means is in an"off"mode.

FIG 7b is a schematic side view of the handle shown in Fig 1, showing the locking means and lock release means when the locking is in an"on"mode.

In FIG 1, reference numeral 1 refers to a power tool in accordance with the invention.

The tool 1 comprises broadly a body 2, at the leading end of which is a working head (not shown) and a trigger handle 3. The working head may receive any one of a number of pieces, eg a fastener, drill bit or the like. In an electric power drill the working head is a chuck for removably receiving a suitable drill bit which rotates at high speed during operation of the tool. A power cord extends from the body 2 and trigger handle 3 rearwardly to a power point (not shown). The power cord is electrically connected to an electric motor within the body. As discussed above other forms of power including liquid fuel and compressed air may also be used.

The trigger handle 3 in turn comprises a handle member 4, and a power trigger 5 mounted on the member 4 and squeezable or depressible by the index finger of a user's hand. Beneath and adjacent to the power trigger 5 is a safety trigger 7 so mounted on the handle member 4 in a similar orientation to the power trigger 5. As with the power trigger 5 the safety trigger 7 is squeezable or depressible by at least the second and/or third fingers of a user.

The power trigger 5 is typically of the usual construction one would expect in an electric power tool such as an electric drill. The trigger 5 is moveable rearwardly against a resilient bias of a spring to an activated position in which it closes an activation switch 10. When the activation switch 10 is closed, power is able to flow from the power supply through the working head to drive high speed rotation thereof.

The safety trigger 7 is also moveable rearwardly against the bias of a resilient biasing spring 15 to a release position where it contacts a switch 16. The trigger 7 must also be in the release position before power can flow to the motor that drives the working head. The switch 16 is shown in the drawings as an isolating micro switch. The

resilient biasing spring 15 may conveniently be in the form of a helical coil spring acting under compression between surfaces on each of the safety trigger 7 and the handle member 4.

In addition the safety trigger 7 includes or has associated with it a blocking means in the form of a pivotal block 20. The block 20 acts to physically resist or block the movement of the power trigger 5 to the activated position as shown in Figs 2a and 3a unless and until the safety trigger 7 has been depressed to the release position, as shown in Figs 2b and 3b.

With reference to Figs 4-6, the block 20, has a projection 21 that acts against trigger 5 by the bias force provided by dual action spring 23. The block 20 comprises an upper member 20a from which projection 21 extends, and a lower member 20b. The surfaces of block 20 are configured to complement respectively the safety trigger 7 and power trigger 5.

The tool 1 also includes locking means in the form of a mechanism 30 for locking the power and safety triggers 5 and 7 in respectively the activated and release positions when the tool 1 is in full operation.

The detail of this mechanism 30 is shown in Figs 7a and 7b. Broadly the mechanism 30 comprises a manually operable toggle 32 operatively connected to trigger locking elements 34 and 35 for each of the power and safety triggers by means of linkages 37 and 38 as shown in Fig 2.

Each of the locking elements 34,35 is movably mounted on the linkage mechanism 30 so it can move both into and out of engagement with the triggers 5,7.

Each element 34,35 has a respective recess adapted to engage with a respective pin 41,42 on triggers 5,7.

The toggle 32 is pivotally mounted on the handle member 4 and is pivotal between "off"and"on"positions. The toggle 32 is biased towards the"off"position by a torsion spring 50 as shown in Fig 7a.

The mechanism 30 also includes release means for releasing toggle 32 permitting it to move back to the off position when there is any manual movement of either trigger 5

of 7. When the toggle 32 is in the locked positioned as shown in Fig 7b, the pins 41 and 42 are engaged with the respective recesses on elements 34,35 and spring 51 is held in tension. The shape and size of pins 41,42 and the associated recesses are such that manual movement of either trigger 5,7 will result in the pins 41,42 disengaging from their respective recesses and allowing spring 51 to relax. This will then allow the bias of torsion spring 50 to urge linkage mechanism 30 and toggle 32 to the"off" position shown in 7a.

In use a user will take hold of the tool in at least one hand and connect the power cord to a power supply. The activation switch 10 cannot be moved to the activated position until the micro switch 16 has been moved to the release position. To do this the safety trigger 7 must be squeezed and depressed against the bias of the spring 15 to the release position in which the switch 16 is closed. When this occurs current can flow through a circuit to the activation switch 10 of the power trigger 5. When the activation switch 10 is closed power is able to flow from the power supply through to the drive means for the tool, eg an electric motor, received in the body 2 of the tool 1. This can then drive rotation of the working head.

Further the rearward movement of the safety trigger 7 permits the block 20 to be pivotally moved away from the power trigger 5 when it is depressed. If the safety trigger 7 has not been depressed then the block 20 will interfere with or block depression of the power trigger 7. The purpose of this feature is to prevent the tool being started under full load which would be dangerous and undesirable.

During normal running operation of the tool after it is operating normally a user can lock the triggers 5,7 in an operating position by manually pushing the toggle 32 from the off to on positions. The user can then focus all their energy on the efficacious operation of the tool. To disengage the trigger locking means they simply apply pressure to either trigger 5,7. This disengages pins 41,42 from elements 34,35 allowing the toggle 32 to move back to the off position to which it is biased.

The strength of the spring 15 for the safety trigger 7 can be selected depending on the strength required by the user to handle the tool 1. For example for a small light weight tool suitable for domestic use can be safely handled by a person of less than average strength, a relatively soft spring 15 that is easily compressed may be used. By

contrast for a heavy powerful tool requiring a strong and skilled user a strong spring 15 that requires a greater force to compress may be used. This ensures that the tool can only be activated and switched on by a person having quite considerable strength. A development on this feature is that power tools generally may be graded according to their power and different springs having different compression strengths may be used for each grading. This will ensure that the safety trigger 7 in any tool requires an appropriate level of finger and hand strength to depress the trigger 7 before it is used.

An advantage of the power tool with safety trigger 7 described above is that it helps to make sure that the tool is being securely held before the trigger 5 can close the activation switch 10 and full power can flow to the motor of the tool. It also reduces the chance that a small child will activate a power tool because of the reasonably sophisticated and complex starting operation. It requires depression of the safety trigger 7 first by the second and/or third fingers and then the power trigger 5 by the index finger.

It also requires the safety trigger to be held depressed while the power trigger 5 is squeezed. This requires a reasonable level of strength and coordination and also a knowledge of the starting procedure.

A further advantage of the tool is that by suitable calibration of the safety trigger spring 15, the safety trigger 7 can make it difficult for a person having insufficient strength to safely operate the tool to get it started. That is the safety trigger 7 requires a threshold level of strength commensurate with that required to operate the machine, before a user can get the tool started.

Further the safety trigger 7 is neutral to both left and right handers. It enables an operator to operate the safety trigger 7 equally with their left and right hand.

A further advantage is that the tool has a blocking means that prevents the power trigger 5 being depressed first and then the safety trigger second. Such a situation would lead to the tool being started under full load which would be undesirable.

A further advantage is that the tool has a locking means in the form of a toggle that permits a machine to be locked in an"on"running mode. This permits an operator to let go of the power and safety triggers 5,7 during operation and essentially operate in a

hands free manner. The toggle 32 is automatically released or cancelled when any pressure is applied to the safety trigger 7 or the power trigger 5 of the tool.

The type of power used to drive the tool 1 in this embodiment is by domestic mains power supply. It may in another embodiment be powered by an internal battery.

Alternatively in another embodiment the power may be provided by compressed air that for example is used to drive a jack hammer. Further alternatively the power may be provided by a fuel driven internal combustion engine. An example of this is a portable cutting device.

It will of course be realised that the above has been given only by way of illustrative example of the invention and that all such modifications and variations thereto as would be apparent to persons skilled in the art are deemed to fall within the broad scope and ambit of the invention as is herein set forth.

The term"comprising" (and its grammatical variations) as used herein is used in the inclusive sense of"having"or"including"and not in the exclusive sense of "consisting only of".