GB2201324A

GB2201324A - Powered garden tools

Info

Publication number: GB2201324A
Application number: GB08703412A
Authority: GB
Inventors: Michael Veveris; Peter Beaumont
Original assignee: QUALCAST GARDEN PROD
Current assignee: QUALCAST GARDEN PROD
Priority date: 1987-02-13
Filing date: 1987-02-13
Publication date: 1988-09-01
Also published as: GB8703412D0

Abstract

A cutter mechanism for a powered garden tool, such as a lawn edge trimmer, comprises a pair of relatively movable cooperating blades (13, 14), drive means including a drive transmitting member (12) coupled to a movable one (13) of the blades in such a manner that the coupling (59, 59a) is partially released whenever the load on the moving blade exceeds a predetermined level, and means (30, 31) for controlling the displacement of the movable blade (13) in its partially released state such that the coupling (59, 59a) is fully restored in response to the displacement of the blade when the excess load is removed. The coupling comprises pips 59, 59a on blade 13 engaging in apertures 60 in member 12, one pip 59 being shaped to release from its aperture at the predetermined load. The blade 13 thereafter pivoting about pip 59a, the movement being limited by raised tang 31 on blade 13 engaging the edge of member 12. <IMAGE>

Description

POWERED GARDEN TOOLS This invention relates to a powered garden tool, particularly an edge trimmer for attachment to a cylinder lawnmower.

When operating powered lawn edge trimmers or other vegetation trimmers of the type having cooperating blades with fingers which slide over one another to perform a shear cutting action, it occasionally happens that a stone or twig becomes jammed between two of the fingers.

This may either stall the motor or risk damage to the drive mechanism. Some form of overload protection is therefore desirable.

One possible form of protection is to provide relatively flexible blade fingers which are able to ride over the jammed obstacle as described, for example, in US Patent 3,623,223. However, such blades are capable of only relatively light duty trimming.

A more robust protective mechanism is described in our copending application 8618865. In this mechanism the drive means to the blades includes a drive transmitting member coupled to a movable one of the blades in such a manner that the coupling is at least partially released whenever the load on the moving blade exceeds a predetermined level.

According to the present invention the coupling of the moving blade to the drive transmitting member is partially released in response to the excess load, and additional means are provided for controlling the displacement of the moving blade in its partially released state such that the coupling is fully restored in response to the said displacement when the excess load is removed.

The protective mechanism is therefore self-correcting and the tool is able to operate continuously without interruption of the power supply even when excessive loads are encountered.

In a preferred embodiment of the invention, the drive transmitting member is resiliently urged against the moving blade, and the coupling between the two members includes a first coupling which is disengaged in response to the excess load and a second coupling which remains engaged and about which the moving blade is free to pivot when the first coupling is disengaged. Stop means are then provided to Limit the displacement of the moving blade such that, when disengaged from the first coupling, the blade is pivoted about the second coupling to a position at which the first coupling is re-engaged.

The first and second couplings may each comprise a protuberance on one of the members received in an opening in the other member, the reaction force on the protuberance of the first coupling when the load exceeds the said level having a component which overcomes the resilient biasing force and thereby urges the protuberance out of the opening. The moving blade then continues to operate with reduced efficiency with only the second protuberance engaged in its opening until the blade strikes a stop which forces it to pivot about the second protuberance and thereby brings the first protuberance back into alignment with its opening.

The tool may comprise, for example, a vegetation trimmer, the blades being of the type waving fingers which slide over one another to perform a shear cutting action. In this case the first coupling is released whenever an obstacle is jammed between a moving blade finger and a fixed blade finger.

The drive transmitting member is preferably actuable between a first tensioned state in which it resiliently urges the moving blade against the fixed blade, and a second relaxed state permitting removal and replacement of the moving and/or fixed blades.

The drive transmitting member may comprise a drive plate which reciprocates about a pivot pin, the tool including a manually operable lever for axially displacing the pivot pin to actuate the drive plate between its relaxed state and its tensioned state.

In the accompanying drawings, by way of example only: Figure 1 is a plan view of an edge trimmer for attachment to a cylinder lawnmower; Figure 2 is a side elevation of the trimmer; Figure 3 is a magnified section on line B-B of Figure 1; Figure 4 is a section on line A-A in Figure 1: Figure 5 is a plan view of the blade driving plate in the trimmer of Figures 1 to 4; Figure 6 is a plan view of the moving cutter blade in the edge trimmer; Figure 7 is a side view of the blade sl.own in Figure 6; Figure 8 is an enlarged section on line C-C in Figure 6; Figure 9 is a diagram-illustrating the forces acting on the locating pips of the moving blade, and Figure 10 is an enlarged section on line B-B in Figure 6.

As shown in thee figures, the edge trimmer comprises a body 1 provided with a plastic wear plate 2 which retains a ball bearing 3 rotatably mounting the spindle 4 of a driven gear wheel 5. The edge trimmer is designed as an accessory for a motor driven cylinder lawnmower. In use, the large diameter gear 50 of the gear wheel 5 is 'plugged' into a clutch pulley mechanism (not shown) in the drive mechanism of the lawnmower. As more fully described and iliustrated in our capending application 8618863, the plugging-in of the gear wheel 5 axially displaces a clutch member against a resilient bias such that drive is transferred from the cutting cylinder of the lawnmower to the present edge trimmer.

The plug-in mounting of the trimmer is more fully described and separately claimed in our copending application 8618864.

The use of the plastic wear plate 2 accommodates a certain tolerance in the position of the gear wheel 5 by providing a flexible mounting for the ball bearing 3.

This further simplifies the plug-in mounting of the trimmer.

The small diameter gear 51 of the gear wheel 5 meshes with a gear 18 having its spindle 10 rotatably mounted in upper and lower bushes 9a, 9b. The meshing teeth are provided with sufficient backlash to accommodate the movement of-the gear 51 in its flexible mounting. The lower bush 9b is located in the body 1 of the trimmer while the upper bush 9a is carried by a bridge plate 11 which spans the opposing side walls 53 of the body as shown most clearly in Figure 4.

The gear 18 carries an offset hardened metal roller cam 6 rotatably mounted on a bush 7 carried by a spindle 8.

This cam is located in the yoke 54 (Figure 5) of a pivotally mounted drive plate 12 such that rotation of the gear 18 produces a reciprocating motion of the plate 12 about its pivot pin 16.

The rear end of the plate 12 rests on a ball bearing 9 located in a slot in the wear plate 2, the ball providing a low friction support with a metal shim 20 being positioned beneath the ball to prevent undue wear.

The driving plate 12 releasably engages a moving cutter blade 13 when two pips 59 and 59a (Figures 6-8) on the cutter blade are located-in respective apertures 60 in the plate 12. The reciprocating movement of- blade 13 relative to a fixed blade 14 produces a shear cutting action between the blade fingers.

As shown most clearly in Figure 5, the plate 12 includes a cut-out portion providing a resilient tongue 55 with a hole 56 for receiving the pivot pin 16, the head 57 of the pin being retained against a washer 15. Accordingly the plate 12 is tensioned by pulling down on the pin 16 using a manually operated lever mechanism attached to the lower end of the pin.

The lower end of the pin 16 is T-shaped and the lever mechanism includes a bifurcated lever 17 which receives and retains the T-bar at the lower end of the pin, the lever 17 being movable between its flat closed position shown in Figures 1 to 3 to an open position in which it extends outwardly from the body 1 of the trimmer.

Movement from the open position to the closed position is accompanied by a downward axial movement of the pin 16 with a snap-action due to interaction between ramped bifurcated ends 58 of the lever and the body l. The downward axial movement of pin 16 tensions the plate 12 against the moving cutter blade 13 by pulling down the resilient tongue 55. Subsequent reverse movement of the lever 17 into its open position releases the tension and thereby allows removal of the blade 13 by lifting it clear of the pips 59 and 59a. The fixed blade 14 is also removable when the tension is released since it is merely clamped between the moving blade and the body 1 bv the tensioned plate 12, the fixed blade having openings for receiving fixed locating studs 93 forming an integral part of the body 1.

As shown in Fig. 7, the rear portion of the movable blade 13 includes a joggle or crank 94 to provide the blade with a resilient set.

Should an obstruction become trapped between any two fingers of the cutter blades, this produces a sharp increase in the reaction force in the plane of the blades at each of the pips 59 and 59a. As best shown in Figure 8, the pip 59 has a truncated conical shape which preferably complements the sides of the respective flared circular hole 60. As further shown diagrammatically in Figure 9, the reaction force A on the pip 59 can be resolved into two mutually perpendicular components B and C, the component B being directed into the sloping face of the pip and the component C being directed upwardly along the sloping face. There will also be a downward vertical force X corresponding to the force exerted by the plate 12 when tensioned by the -lever 17.The force X can also be resolved into two components Y and Z, the component Y acting in the same direction as the component B, and the component Z acting down the slope of the pip against the component C of the reaction force.

The sharp increase in the reaction force A when an obstruction becomes trapped between the fingers of the blades results in the component C increasing to a point where it exceeds the component Z and the plate 12 therefore lifts off the pip 59.

This prevents damage to the drive mechanism and generally releases the clamping force on the obstruction. As shown in Figure 10, however, the pip 59a is virtually straightsided (although it may include a 50 taper) and therefore remains located within its respective opening 60.

Accordingly the drive from plate 12 now produces a pivotal movement of the blade 13 about the pip 59a. A raised tang 31 on the moving blade 13 prevents excessive pivotal movement in one direction by engaging the edge of drive plate 12. Under no circumstances therefore is the pip 59 able to come out from under the drive plate without first releasing the tension by actuating lever 17.

At the same time the extremes of movement of the moving blade fingers 15 as the driving plate 12 continues to oscillate back and forth about its pivot are set by a pair of raised part shears 30a, 30b on the outermost fingers 90, 91 of the fixed blade 14. The combined action of the moving blade fingers striking one or other of the part shears 30a, 30b and the pivotal movement of the moving blade about the pip 59a therefore urges the pip 59 back into alignment with its respective opening 60 in the drive plate.

This self-correcting mechanism gives the advantage of automatic and substantially instantaneous re-location of the moving blade once the obstruction has been removed.

Claims

1. A cutter mechanism for a powered garden tool, the mechanism comprising a pair of relatively moyable cooperating blades, drive means including a drive transmitting member coupled to a movable one of the blades in such a manner that the coupling is partially released whenever the load on the blade exceeds a predetermined level, and means for controlling the displacement of the movable blade in its partially released state such that the coupling is fully restored in response to the said displacement when the excess load is removed.

2. A mechanism according to claim 1 in which the coupling between the two members includes a first coupling which is disengaged in response to the excess load, and a second coupling which remains engaged and about which the moving blade is free to pivot when the first coupling is disengaged.

3. A mechanism according to claim 2 further comprising stop means for limiting the displacement of the moving blade such that, when disengaged from the first coupling, the blade pivots about the second coupling back toward a position at which the first coupling is re-engaged.

4. A mechanism according to claim 3 in which the first and second couplings each comprise a protuberance on one of the members received in an opening in the other member, the reaction force on the protuberance of the first coupling when the load exceeds the said level having a component which overcomes a resilient biasing force and thereby urges the protuberance out of the opening.

5. A mechansim according to any one of the preceding claims in which the cooperating blades each have fingers which slide over one another to perform a shear cutting action.

6. A mechanism according to claim 5 in which one of the brads liy movable and the other is fixed, and in which the drive transmitting member is actuable between a first tensioned state in which it resiliently urges the moving blade against the fixed blade and a second relaxed state permitting removal and replacement of the moving and/or fixed blades.

7. A mechanism according to claim 6 in which the drive transmitting member comprises a drive plate which reciprocates about a pivot pin, the mechanism including a manually operable lever for axially displacing the pivot pin to actuate the drive plate between it relaxed state and it tensioned state.

8. A powered garden tool including a cutting mechanism according to any one of the preceding claims.

9. A lawn edge trimmer including a cutter mechanism according to any one of the claims 1-7.

10. A lawn edge trimmer according to claim 9 in which the cutter mechanism is disposed within a housing adapted for releasable attachment to a powered cylinder lawn mower whereby the drive means of the cutter mechanism is connected to a drive transmission member of the lawn mower.