GB2187410A - Hand operated pruners and the like cutting and gripping tools - Google Patents

Abstract

A garden pruner provides two modes of operation. The first or direct mode closes the cutting blades 2, 3 by scissors action in which the clenching force of the hand is directly transferred to the cutting blades 2, 3. The second or ratio mode introduces mechanical amplification to the pruner action so that the force provided at the cutting blades 2, 3 is considerably increased for the same hand grip as before. An adjustable break-clutch 17, 18 is employed to automatically change the pruner action from the first to the second mode if the effort required to sever a plant stem placed between the blades is greater than can be achieved by the hand grip of the operator while the pruner is operating in the first mode. This principle may also be applied to hand tools for other purposes which have cutting or gripping blades. <IMAGE>

Description

SPECIFICATION Pruners This invention relates to garden and horticultural pruners.

Existing hand pruners operate by direct scissors action between the hand grips and the cutting blades. The cutting force which can be transmitted is therefore limited by the grip the user is capable of exerting, without any improvement beyond the simple leverage of the handles ofthetool. For most users this is adequate to cut soft stemmed plants and small shrubs, however cutting hardwood stems becomes more difficult. If the user is elderly or suffers from any muscular impediment, then the use of these pru ners, even fo r softer stem med plants becomes difficult.

It is the purpose ofthe present invention to provide a pruner with an improved action.

Accordingly the present invention provides a pruner having two modes of operation. The first, or direct mode is conventional, the operation of the pruner being by scissors action with the clenching force of the hand directly transferred to the cutting blades. The second, or ratio mode introduces mechanical amplification to the action so thatthe force atthe cutting blades is nowconsiderably increased forthe same hand grip as before.

When the second mode is being used it is necessary to clench and release the pruner handles a number of times to obtain full cutting blade travel.

Because ofthis it is more convenient to use the direct mode for easily cut, soft stemmed plants.

The change over from direct to ratio action is automatic when the maximum force which can be exerted by the operator is reached. In order to cater forthecapabilitiesofall users, the gripping force at the point of changeover is adjustable, thus people with infirmities can set the changeover at a low level, while more robust users can operate on harder stems while still in the direct mode.

It is envisaged that a pruner of the present invention may have a first handle to which is attached a fixed cutting blade. This handle also contains towards the blade end a pivot about which a second, moveable cutting blade rotates.

Rotating about the same pivot is a second handle which is connected to the second cutting blade by means of a brake-clutch.

Mounted within the first handle is a transfer shaft, which projects from the end of the handle adjacentto the moving blade, and is attached to the moving blade by means of a further pivot. A compression spring is provided between the first handle and the transfer shaft, which acts to return the transfer shaft when it has been displaced to it's rest position which corresponds to the fully open position of the moving blade.

The fixed handle may also contain a means for advancing the transfer shaft longitudinally comprising a one way gripper, arranged so that it will reciprocate in the direction of travel of the shaft between a shaft gripping position on the forward stroke of reciprocation and a shaft release position on the return stroke.

Also mounted within the fixed handle may be a catch, intended to prevent return motion ofthe transfer shaft as it is displaced by the gripper. This catch is normally rendered inoperative by means of a spring latch attached to the gripper, and will only be activated when the gripper itself is operated.

The moving handle of the pruner contains a projection which bears against the rearward side of the gripper when the handle is moved afterthe break-clutch has disengaged. Movement of the handle under this circumstance maythen reciprocate the gripper causing the transfer shaftto move in a direction to close the second blade.

In operation, movement of the second handle towards the first handle moves the second blade, via the break-clutch, towards the fixed cutting blade. As the second blade moves it causes the transfer shaft to compress the compression spring and upon releasing the second handle the compression spring expands, causing the second handle and the moving bladeto return once moretothefullyopen position.

Any stem placed between the blades which requires lesseffortto cut than is required to disengagethe break-clutch will beseveredina conventional way, the pruner having operated in the direct mode.

if the stem being cut requires more effort than can be transmitted by the break-clutch, this disengages, allowing the second handle to move towards the first handle independently from the cutting blade. The pruner has now changed to the ratio mode of operation.

The projection on the moving handle now operates the one way gripper, causing the transfer shaft to move a small amount, and in turn causing the second blade to move a small distance towards the fixed blade. It will be shown that this action produces a greaterforcethanthatpreviously achieved in the direct mode.

Movementofthe gripper causes the catch to activate, preventing return movement of the transfer shaft when the moving handle is released.

Repeated action of the moving handle causes repeated small movements ofthe moving blade until the plant stem.between the two blades is completely severed. At the completion ofthe blade travel the break-clutch automatically re-engages, and the pruner revertstothe direct mode of operation.

A small extension provided on the catch, which extends outside the fixed handle surface, may now be pressed by the user of the pruner. This releases the catch allowing the pruner blades to move once moreto the fully open position, and at the sametime latches the catch to the gripper, rendering the catch inoperative again until sometime as the pruner changes once more to the ratio mode of operation.

The invention may be carried into practice in a number of ways, but one embodiment will now be described bywayof example, andwith referenceto the accompanying drawings in which: Figure lisa side view of a prunqr in accordance with the invention.

Figure2 is a cross section of the pruner shown in figure 1.

Figure 3 is a perspective exploded view of the break-clutch members.

Figure4shows the forces produced on and by the various members of the prunerwhen in use, the directions in which they operate, and important dimensions.

Referring to the drawings, there is shown a fixed handle 1 containing a fixed cutting blade 2 secured to it atone end.

Moving cutting blade 3 is pivoted on handle 1 at4.

Also pivoted atthis point is moving handle 5.

Contained within fixed handle 1 is transfer shaft 6, transfer shaft return spring 7, one waygripper8, gripper return spring 9, catch 10 and catch operating spring 11.

Catch 10 is pivoted about point 12. Latch spring 13 projects through a hole in catch 10, and holds catch 10 in the position shown when it has been pressed downwards by means of extension 14which projects through hole 15 in the surface of fixed handle 1.

Transfer shaft is attached to moving blade 3 by means of pivot 16.

The periphery of moving blade 3 contains detent notches 17, which are more easily seen in figure 3.

Moving handle 5 is coupled to moving blade 2 by meansofdetent pin 18 cooperating with detent notches 17, Detent pin 18 is held in position by compression spring 19 which is itself secured by threaded pin 20.

Threaded pin 20 may be wound in orouttovary the force produced on detent pin 17 which in turn adjuststhemaximumtorquewhichcan be transmitted by the break-clutch assembly before it disengages.

Gripper 8 contains a hole through which transfer shaft 6 passes, and which is slightly larger in diameterthan the shaft. In the position shown in figure 2 the gripper is pressed against web 23 which is part of handle 1, by the action of return spring 9, and held atright angles to the axis of the shaft. In this attitude, movement of the transfer shaftto and fro is unimpeded, however, if projection 21 on moving handle Snow exerts pressure on gripper body 8 at point 22, the gripper will tilt until it becomes tight on the transfer shaft. Further movement of projection 21 to the right will now cause both the gripper and the transfer shaft to move to the right with a force equal to that being exerted by projection 21 at point 22.

As the gripper moves to the right, it moves latch 13 with it, and this in turn releases catch 10.

Catch 10 also contains a hole through which transfer shaft6 passes, and this is also slightly larger in diameterthan the shaft.

Before it is released catch 10 is held at rightang les to the transfer shaft axis and presents no impedimentto transfer shaft movement in either direction, however once released it pivots about point 12 underthe influence of spring 11 until it grips the transfer shaft. In this position it will permit transfershaft movementtothe right, but prevent return movement to the left.

Thus when pressure from projection 21 on gripper 8 at point 22 is removed, gYipper 8 returns to it's rest position but transfer shaft 6 is prevented from return motion bytheaction of release catch 10.

Figure 2 shows the pruner mechanism operating in the direct mode. When handle 5 is pulled towards handle 1 ittransmitsthis movementvia pin 18 and detent notches 17to moving blade 3.

By the time handle 5 reaches the position B shown in figure 1 the moving blade has travelled all the way towards fixed blade 2. Any object placed between the two blades will have been completely severed provided the effort required to do this is no greater than that capable of being transmitted at the junction of plunger 18 on the handle 5 and the notches 17 on the moving blade 3.

If the effort necessary to cut the object between the cutting blades is greaterthan can be transmitted in direct mode, plunger 18 is forced backwards until it jumps out of the notches 17, thus releasing the handle 5 from the moving blade 3. This changes the pruner action overto the second, ratio mode.

Handle Snow rotates towards handle 1 without moving blade 3 until projection 21 comes into contact with the rear face of gripper8 at point 22.

This occurs just afterthe handle has passed position B shown in figure 1.

Further movement of handle 5 now causes gripper 8to tilt until ittightensontransfer shaft 6, and still further movement causes the gripper and transfer shaft to move together towards the right, partially closing moving blade 3 as they do so. When the moving handle has reached position C in figure 1 it is released, whereupon it returns to position B under the influence of gripper return spring 9, however catch 10 prevents any return movement of transfer shaft 6, which remains partially extended.

Repeated movements of handle 5 between positions B and C incrementally move transfer shaft 6 out of handle 1, in turn causing moving blade3 gradually to close against the fixed blade 2.

Figure 3 shows the forces exerted on and bythe pruner and some of it's dimensions.

If FD represents the cutting force obtainable in the direct mode of action, and FR theforce in the ratio mode, it can be shown that FR = Fn x R/r Thusforexample if R = 30 mm and r = 10 mm, FR wil be 3 x FD. This means that operation in the ratio mode will produce three times the cutting force for the same hand grip as was exerted in the direct mode.

These dimensions are by way of illustration only and may be altered in practice to produce otherforce ratios.

When the handle is released afterthefinal movement of blade 3, it returns to position B, whereupon plunger 18springs back into notches 17 and the pruner reverts once again to the direct mode of operation.

The fully closed blades may now be released by depressing the extension 14to catch 10. This action releases transfer shaft 6, which returns to the rest position underthe influence of spring 7, and in so doing fully opens moving blade 3 once more. Atthe same time catch 10 is returned to it's inoperative position by latch 13.

It will be appreciated that the embodiment of the invention described above has been given by way of example only and that modifications may be effected. Thus, for example, the shape of the pruner blades may be curved instead of straight and the break-clutch may be of different design. Also other applications are possible so that a version of the apparatus may be designedforexampleto cutwires and cables.

Claims (9)

1. A garden pruner or other hand tool comprising a pair of handles or levers pivoted together and operating cutting or gripping blades, the blade moved by one of the levers being connected to that lever by means of a break-clutch which when engaged causes both blades to close together by direct scissors action but when disengaged permits this lever to move independently of its associated blade and in so doing activate and operate an alternative blade drive which now causes the blades to closetogetherwith increased force.

2. A garden pruner or other hand tool as claimed in Claim 1 in which the alternative drive is obtained by means of a transfer shaft attached to the break-clutch associated blade by means of a flexible coupling.

3. Agarden pruner or other hand tool as claimed in Claims 1 and 2 in which movement of the transfer shaft in either direction is unimpeded when the tool is being operated with the break-clutch engaged.

4. A pruner or other hand tool as claimed in previous claims in which disengagement of the break-clutch permits the alternative drive to be operated by means of a one way gripper arranged to fit round the transfer shaft and reciprocate along the axis ofthe shaft and to tilt relative to the axis ofthe shaft between a gripping position on the forward stroke to advance the shaft to cause the blades to close together and a releasing position on the return stroke of the reciprocating gripper,

5. A pruner or other hand tool as claimed in Claim 4 in which reciprocation of the one way gripper is obtained in the gripping direction by means of a projection on or a rod attached to the releasable lever and in the shaft release direction by means of a return spring.

6. A pruner or other hand tool as claimed in Claim 5 inwhich the oneway gripper is notoperated until the lever released by the disengaged break-clutch has moved beyond the position it occupies when in its engaged condition the blades are fully closed.

7. Aprunerorother handtool as claimed in Claims 5 and 6 in which a spring biased catch is provided to prevent movement of the transfer shaft in the blade opening direction when the one way gripper is returning to its rest position underthe influence ofthe return spring, and also in which a latch is provided to hold the spring biased catch in a non-operational position when the tool is being used with the break-clutch engaged, but in which the latch is caused to move and release the spring biased catch so that it wil I operate when afterthe break-clutch has released the disengaged lever has moved beyond the position it occupies when in its engaged condition the blades are fully closed.

8. Aprunerorotherhandtool as claimed previous claims in which the efforttransmitted by the break-clutch can be varied by means of an adjustable spring.

9. Agarden prunerorother hand tool containing cutting or gripping blades substantially as described herein with reference to Figures 1-4 of the accompanying drawing.